I'll have to exclude 1-5 from my list since it's been absolute ages since I listened to those.
Disclaimer: Judging these not by in-game, but out-of-game. (this matters a lot in some themes' cases, such as the exploration theme in FFXV being interrupted by random crap all the time in-game, not allowing you to actually hear the theme properly)

10. XII
9. X
8. XIII
7. VII
6. VI
5. VIII
4. IX
3. XV
2. XI
1. XIV

Note: XI and XIV kind of cheat because their expansions also expand their music selection.