The only Final Fantasy vocal theme song I've enjoyed is Suteki Da Ne. I can't really explain it; it's not that it remained untranslated, I just never quite picked up on any of the others.

Eyes On Me was okay, I guess. Nothing special.
Melodies of Life was incredibly annoying by the time you finally get to hear it with lyrics. I swear, every second song in the game has the same tune. Regardless, it's still my favorite soundtrack. That's besides the point.
Do I really need to comment on the songs in FFX-2? I just don't really like the whole generic pop thing.
Kiss Me Goodbye was oddly out of place in FFXII.

Edit: Aria De Mezzo Caratter (the orchestrated version with actual vocals) is pretty damn awesome, too, if you want to count that.