Ahhh, we are talking about SMF playback etc?? Well, I would say GeneralMusic does that the best, its got to be said. If there is a keyboard that I have owned and noted for its strength, it would have to be GEM for midi & SMF playback. The worst in my opinion is the Korg I series, they just sound so electronic and totally unnatural.
Of course, each keyboard that has its own programmed SMF sequences will not sound the same elsewhere but only best where it was originally programmed. But if you want to test how good your SMF playback is on your own keyboard, try the TUNE1000 songs, that will test the sequencer!
Ketron SD60, Ketron SD7, Korg Pa1000, Ketron Audya, Yamaha SX900, Yamaha Tyros4