FFX's battle system is probably my favorite of all of the FFs. While VIII's my most hated. So in that regard X wins easily. I liked VIII's setting more and I liked it's story more until the huge plot twists that even disrupt your suspension of disbelief. Characters is a slight win for X. Laguna being the only reason it's close. lol. So overall, X wins for me.

EDIT: Actually, even with the unbelievable plot twists. VIII's story is better. But X still wins overall.