That's two from FFXIII-2, though surely if there was a number six I would have put Eternity. Honestly it just depends on what kind of mood I'm in. They flipflop all the time! A track from FFV could even sneak its way up there at the right moment. If I could rank my favorite soundtracks:

1. FFXIII
2. FFXIII-2
3. FFX
4. FFVIII
5. FFX-2
6. FFXII
7. FFV
8. FFIX
9. FFVII

The others are pleasant enough, but I never purposely listen to them.