I say orchestrated.
If this was a contest on which music is catchier, then MIDI would win hands down. However, ot os mpt/ The question clearly states which kind of music you like best. And, as a musician, I have to say that cathy does not always mean better. Nothing beats real instruments in my books, no matter how good the music is. Skyward Sword's soundtrack gives me a sense of emotion that I don't get from any of the other soundtracks, and this is because it is real. I would much rather listen to a slow, 3 hour symphony than any MIDI oriented music. Live orchestrations are just so much more impressive and have a much grander sound than the MIDIs, and I think it fits the series better. Now don't get me wrong, as I love MIDI music as well; there's just nothing quite like listening to real instruments in the background of one of my favourite games.
So basically: Orchestrated > MIDI.
Don't think I excluded the music from the 8/16 bit eras. They are MIDIs as well.