Warmachine/Tactics/Differences between Warmachine and 40k
Overarching Differences
The biggest difference between the games is that a typical Warmahordes game will go for 20-40 minutes whereas a Warhammer game is more likely to go for 1-2 hours or longer. Additionally if budget is your biggest concern Warmahordes is far superior. Due to these two differences alone Warmahordes lends itself to being a more casual player friendly game and you don't feel quite so much like Satan when convincing your friends to get into it as you do for Warhammer. On a side note if you're looking for cheap tabletop models I've always found Discount_Games_Store on Ebay to be the best place to buy cheap, unassembled models (not affiliated in any way).
Warmahordes is, in general more comparable to Warhammer Fantasy than 40k in so far as generally speaking ranged weapons are less potent/more volatile as a strategy. In most armies ranged weapons are used to soften the enemy up for the melee big hitters, there are very few factions that can hope to field a shooting only army and win. This is mostly because in general shooting attacks are much weaker than melee attacks and many armies have special rules that make their troops hard to hit with ranged attacks. Another way in which Warmahordes is more comparable to Fantasy is that the general theme is older technology rather than futuristic although Warmahordes tends to float around the 1400s where Fantasy sits more in the feudal days. Finally the warcaster or warlock (Warmahordes' version of the HQ) is much more important than in 40k such that in the typical gameplay type if the warcaster or warlock bites the dust the game is over.
Cost and Models
A major difference is the model count and real money cost of the games. Whilst a proactive buyer may be able to get a competitive Warhammer army from ebay for fairly cheap (talking maybe $300), an army that is ready to play can cost as little as $60 for Warmahordes, although a proper 35 point game will more likely set you back around $150-2500. In Warmahordes the typical model count can vary between 4-50 whereas in Warhammer that can be in a single unit. Warmahordes is much more favourable to variety than Warhammer such that almost all units are viable one way or another and in the case of most armies if two different people bring the same faction their lists will likely not even share a common unit. In Warhammer however many races have must take units and sometimes even have a specific list to take if the player wants to have a chance in a tournament.
Also in Warmahordes by and large there is NO CUSTOMIZATION. With many light to medium units you can choose whether you want a smaller or a larger unit e.g. 4 OR 6 and with many units you can choose to take a Unit Attachment which offers a variety of bonuses. Aside from this there is NO CUSTOMIZATION. You cannot swap out a model's weapon, you cannot elect to drop a special rule for a point consolidation and you cannot deck your HQ out with sick ass weapons, in many ways this is by design to aid with balancing.
Rolling
Finally a major difference is the way the dice are rolled in Warmahordes. In Warhammer almost all rolls go off a 1d6 system which is an even distribution on each individual roll which can cause crippling clusters of random number generation when very few dice are being rolled. The system works well with units that have large numbers of dice rolls such as Ork or Tau rank and file but becomes risky at best when rolling important rolls for expensive models such as losing the blast from a Riptide on the gets hot roll. Warmahordes has somewhat mitigated this risk (thus enabling less infuriating gameplay with a low model count) by utilizing a 2d6 system on almost all dice rolls and often having the option to "boost" rolls by adding an extra d6. Using the cumulative total from multiple dice on each roll gives a rough approximation of a normal distribution making tactics in general more reliable.
Additionally in Warmahordes all rolls (ranged and melee) to hit are made against the target's defence. This is contrast to Warhammer where the to hit roll in shooting was made despite the target's stats taking only the shooter's BS into account. The end result is that in Warmahordes a model's survivability is not purely dependant on its heath or amour but also on its defence(difficulty to be hit).
Wounds/Boxes and Armour
In Warhammer a typical model has 1 wound with the toughest of models having around 5-6, generally speaking (in the absence of special rules) only 1 wound may be taken of by each attack or shot. In Warmahordes most light infantry have only a single wound (wounds are referred to as boxes in Warmahordes), most heavy infantry have multiple around 4-8 and most Warjacks or Warbeasts have in the range of 25-36 working more like health than wounds in Warhammer. In many cases if the larger models (Warbeasts or Warjacks) are hit they can be damaged reducing their combat or utility abilities in future turns unless healed.
In Warhammer 40k armour works as a set armour roll that the model either gets or does not. A success means the model lives with no penalty and a failure means the model either dies or loses a wound. In Warmahordes armour is not rolled, instead the model takes damage if the damage of the hit is higher than the models armour, the model will then take the difference in damage.
Activation
Unlike in Warhammer where all units move and then all units shoot etc. in Warmahordes each unit(not model) takes its full activation individually. For instance if the player chooses to first activate a warjack that warjack will take its movement and then its action, fulfilling all of its special rules before completing its turn. If a unit of 10 models is activated all 10 models will move together and then all 10 models will take their actions together completing their turns. This means that the order in which models are activated generally makes a much larger difference than it does in 40k.
Finally in the absence of special rules models may only make attacks in their own turn in Warmahordes as opposed to 40k where all engaged models make attacks in melee combat.
Typical Stats and Gameplay
Please note everything in this section will be horribly oversimplified for experienced players and is designed to merely give newbies an idea of the gameplay differences. Obviously all of these stats will vary depending on what sort of niche the unit fills. Generally you can assume values higher than those shown are above average and lower are below average.
Warhammer 40k
The typical troop in 40k will have a statline something like this: Weapon Skill 3-4, Ballistic Skill 3-4, Strength 3-4, Toughness 3-4, Wounds 1, Initiative 3-4, Attacks 1, Leadership 7-9, Armour Save 4-5
Whereas a big beasty might have a statline like this: Weapon Skill 3-4, Ballistic Skill 3-4, Strength 6, Toughness 6, Wounds 3-4, Initiative 3-4, Attacks 4, Leadership 7-9, Armour Save 4-5
Vehicles: A vehicles statline works the same except that is has a armour value instead of toughness or an armour save, often has no attack value or initiative and generally moves faster.
A typical range of shooting weapons in 40k is 24".
In the absence of special rules all models move 6 inches.
40k Gameplay
In 40k a model will move in moving phase (generally 6") and then shoot in the shooting phase. The shot will go something like this:
1. Pick a target in range.
2. Roll to hit with a higher chance if the model has a high BS. If the attack misses nothing further.
3. Roll to wound with a higher chance if the strength of the attack was higher than the toughness of the target. If the attack doesn't wound nothing further.
4. The weapon used will either pierce right through the targets armour in which case the target takes a wound and nothing further.
5. Else the weapon does not pierce the targets armour in which case the target rolls an armour save with a higher chance of living if it has a LOWER armour save value. If the the target makes the save nothing further.
6. Else the target takes a wound and nothing further.
7. Depending on how much damage the target unit took it may need to pass a leadership test by rolling lower that its Ld on 2d6 or run away.
Whereas a melee round will go something like this:
1. Two units are in melee.
2. The one with the higher Initiative goes first.
3. Make as many attacks as the models Attack stat.
4. Roll to hit with a higher chance to hit if the models WS is higher than the target. If the attack misses nothing further.
5. Roll to wound with a higher chance if the strength of the attack was higher than the toughness of the target. If the attack doesn't wound nothing further.
6. The attack will either pierce right through the targets armour in which case the target takes a wound and nothing further.
7. Else the weapon does not pierce the targets armour in which case the target rolls an armour save with a higher chance of living if it has a LOWER armour save value. If the the target makes the save nothing further.
8. Else the target takes a wound and nothing further.
9. The unit with the lower initiative makes its attack as described above.
10. The unit that took the most wounds needs to pass a leadership test by rolling lower that its (Leadership - (wounds taken - wounds given)) on 2d6 or run away. Example unit 1 has Ld 8, dealt 7 wounds and took 5. It must roll lower than 6 on 2d6. 6 because its Ld of (8-(7-5))=6.
Against vehicles instead of rolling against toughness d6 is added to the strength of the weapon, if the total is higher than the vehicle's armour the vehicle is damaged.
Warmahordes
The typical troop in Warmahordes will have a statline something like this: Speed 5, Strength + Power 11, Melee Attack 5, Ranged Attack 5, Defense 12, Armour 14, Command 8
Whereas a big beasty might have a statline like this: Speed 5, Strength + Power 14, Melee Attack 5, Ranged Attack 5, Defense 11, Armour 18, Command 8
A typical ranged weapon in Warmahordes can shoot 10".
It's worth noting that because Warmahordes uses 2d6 1 point difference in stats is a much less dramatic difference than in 40k.
Warmahordes Gameplay
In Warmahordes a unit will be activated and then takes its full move (generally its speed) and then make its action. A shooting action will look something like this, note shooting attacks just use power, melee uses strength+power:
1. Pick a target.
2. Measure range, if out of range nothing further.
3. Roll to hit 2d6+RAT. If equal to or higher than the target's defence; hit. Else nothing further.
4. Roll to damage 2d6+Power if the damage is higher than the target's armour the target takes the surplus in damage, else nothing further.
Whereas a melee round will go something like this:
1. Two units are in melee.
2. The one who's turn it is may attack, units may not attack outside of their turn.
3. Make an attack with each of the models weapons, usually 1 with smaller models, usually more with larger models.
4. Roll to hit 2d6+MAT. If equal to or higher than the target's defence; hit. Else nothing further.
5. Roll to damage 2d6+Power+Strength if the damage is higher than the target's armour the target takes the surplus in damage, else nothing further.
Summary
In general Warmahordes is a simpler, smaller game that requires much less money to start. Warmahordes may have a simpler basic rule set but it has many more special rules which more than balances this out. Warmahordes is more melee focused than 40k and the games go for a shorter period of time. Finally the 2d6 system allows for a more predictable outcome of any move which results in a game that often feels less chaotic than 40k.
However Warmahordes is much less customizable then 40k, so making an army of your dudez is much harder. You can't make your own commander with a history all of his own and have to use one of the Warnouns that already exist. Also, the lack of options for the troops makes making what ever fluff you have Crunchy more difficult. Warmahordes feels more like a historical game then a fantasy one in that you're not making your own story so much as stepping into some one else's. Further, Privateer press has pretty tight conversion guide lines for its tournaments, (which to be fair make sense because a lot of things like the Warjacks share the same chassis and differ only in the arms so making sure no one is confused is important) limiting how wildly you can convert your models.
There are two ways to view 40k VS Warmahordes. If you want a casual game, Warmahordes is far superior for these reasons, but if you are prepared to dump a fair amount of time and money for a larger scale game with more battlefield commander feel, you may prefer Warhammer. On the other hand, Warmahordes' greater predictability places more importance on tactics and is a bit better balanced with fewer stand out horrible choices like Pyrovores making it better for people who want greater tactics in their game. 40k rule set (especially with new unbound rules) favor narrative with players expected to play the army they want with the back story they want making it like a RPG war-game hybrid. This is why 40k's plot just keeps treading water, it sets the stage for your Dudes to have epic adventures and story's, while Warmachines' plot advances because they need players willing to reenact events. Historical games like Flames of War or Bolt Action do the same, but as the events are real it's easier to motivate players to play a force from one point of time. Further as has been proven with monstrosities like screamerstar and the Deamon Summoning Tide, 40k is easily broken when taken to high level tournament play with Von, und precisely Von! way to play each of the top level armies.
It's a toss up between which is better and is very much up to personal taste. Thankfully though they're trying to be different things and are not copying each other, so I think there's enough room for both of them.