My favorite is Mystic Quest's. Not only is the regular battle music great, but so is the boss music and the final boss music.

There's a certain battle track out of Tactics I like. It plays at the Fohovam Plains battle. That would be my second choice.

Man with the Machine Gun is third.

FFI's, FFII's, FFVII's, FFX's, and FFXI's are all alright.

The rest I either don't like, or are forgettable. I can however say that at the very bottom of my list is the FFIX regular battle music, boss music, and the FFVI boss music.