I've just started VII, and most of the music I've heard is not incredibly promising, to be honest. The Wall Market theme bothered me. However, I think Blue Fields takes the cake. Even when I thought everything about VIII was perfect, I still hated that song. *shudders*
I was also not a huge fan of the FFX battle theme. Honestly, I think it totally wrecked the mood on a few occasions. I liked X because it was sort of a thought-provoking story (near the end, especially) and so I didn't quite appreciate the blasting brass music in the middle of the beautiful Gagazet theme as they solemnly finish the last leg of the journey. Plus I just heard it a few too many times when I was trying to power up Auron's stupid Masamune...

Wait, was the battle theme even composed by Uematsu, or am I off?