Eternal Steam Engine has to be the best original theme from Hisoutensoku, with Unknown X ~ Unfound Adventure close behind. The Scenery of Living Dolls is so ironic when played when it is, but it's still awesome nonetheless. And an honorable mention to X, the Floating Objects in the Sky just because.
As for remixes, I never really like the remixes from the fighting games, but if I have to choose, then it'll be Voile, the Magic Library.
On another note, does anybody else think the openings to Chinese Tea and SWR's Mystic Oriental Love Consultation are a bit similar?