Well the 'saddest' or 'most emotional' songs in X and X-2 in my opinion are

FFX:
- Ending Theme (At least, parts of it)
- Someday The Dream Will End
- To Zanarkand
- Wandering Flame
- Revealed Truth
There may be more for FFX, perhaps Suteki Da Ne and all that jazz.

FFX-2:
- Eternity (The Intro song)
- Yuna's Ballad
- 1000 Words