I would say that Ketron has the best midi file play back then Roland and then the Genesys.

Notice I said Genesys and not Gem keyboards in general. Gem keyboards before the Genesys really did not do justice to sounds nor midi files. But with the Genesys, it selects the best sounds on the keyboard to play the midi file.

The midjay and Genesys xp are keyboard modules, but there are not in the same league. The XP has much more sounds, styles and features than the midjay thus the difference in price. But with most musical equipment purchases, you really have to look around to get the best deal.