Oh dear! I see someone from the X crowd was foolhardy enough to bring the soundtracks into this! And to think I was going to be so nice and go easy on you...
Well, since that door has opened, I think we can all agree that X has the superior primary battle theme. Boss Theme...debatable, it depends on how much you like Nakano's atmospheric style where nothing really happens. To Zanarkand of course and a few others are absolute classics, I doubt anyone will claim the FFX soundtrack is anything other than sublime.
Trouble is, for every To Zanarkand FFIX has half a dozen You're Not Alone's. For every Yuna's Determination there are two Bran Bals. For every Enemy Attack there was a Vamo Alla Flamenco! It had really catchy world map music. Do you remember FFX's world map music? Oh wait... X didn't have a world map? Shame really. FFIX has one of the all time great soundtracks. There was so much of it in fact they released a second soundtrack in order to get on all the brilliant pieces composed for the game's many FMV sequences. X completely neglected this area, with the notable exception of the Sending scene. But completely lacked anything like, well... this!