There's no doubt that using SMFs gives a more realistic interpretation of the music - if that's what you're looking for. And Roland's COVER feature makes adjusting instruments in an SMF even easier and can make the midi file even more life-like. Having owned Y's, K's and R's I agree with
Donny that Roland is probably the easiest to work with SMFs.

As always, the major limitation to SMFs is the format and length. But most of the newer file players permit marking, jumping and looping of files so that playing extended or abbreviated versions is easier.

I also feel SMF are more for singers than instrumentalists. With the chords structured just like the record, it's sometimes harder to do instrumental solos because the comping chords are missing.