I have... *drumroll* TWO favourite moments in FFX.
1: After the Otherworld-thyng, when you're hounding about Baaj temple. A whole roomfull of atmosphere.
2: *Blink* Some DIDN'T like this moment? Oh well, all the same... The dialogue outside Yunalesca's chamber (aside from when Tidus screws it up) was all that I asked for when I played the game the first time.

... Aaah, phooey! I forgot! I have a THIRD favourite moment (not in any sort of order, mind you)! The cutscene before the second Seymore-fight. How Seymore just pops up like that... *Hiccup*

Hehe, *sweat* now for the worst bit. While I didn't care for Blitzball, I did stay away from it long enough. I never did like the Cloisters of trial. NONE of them. Bevelle in particular. I can't single out any big, singular piece that I didn't like (Whoa! First time in FF-history!)... That is, that I dislike with a vengeance. I suppose Yuna's voice-acting is a big enough issue to mention...