Challenger

I dare say, this page is delightfully British. Spot of tea?

Not to be confused with the Challenger 1 MBT

The Challenger is simply a Cromwell armed with a 17-pdr, just as the Sherman Firefly is to the Sherman. If the derpy turret doesn't make it obvious enough, the Challenger was a stop-gap design aimed at marrying mobility with anti-tank firepower, giving the British a dedicated Tank Destroyer that can keep up with outflanking Cruisers, a role that it continues to take on the Tabletop.

Stats

Gotta Go Fast

Whether you take the Firefly or Challenger basically depends on whether you're taking Shermans or Cromwells, because the Challenger does best leveraging its speed with other Cromwell tanks: the Challenger gives you reliable anti-tank firepower that can threaten other tanks regardless of facing. They do lack HE, like other 17-Pdrs, so any anti-infantry work would have to be done by accompanying vehicles.