The Matilda and Valentine both have a relatively narrow appeal. Of the two, the Matilda II would probably be more popular, because it featured prominently in the early part of the North African campaign and also played a role in the Fall of France (with the BEF), the Eastern Front (with the Soviets, although not very successfully) and the Pacific (the Australians used them up to the end of the war). It would probably be possible for Rubicon to provide all the parts to build the various versions (there were a number of modifications over its service life, and there was a close support version and a flamethrower version).
I think a Churchill would be far more popular, especially if there was an AVRE version included.