Better storyline- Hmm, that's tough, but I'll have to go with Tales of Vesperia. The story is a bit more fleshed out, and the pacing is a bit better (SO:TLH has multi-hour dungeons followed by half hour cutscenes. It's all good, but very lopsided).
Better characters - Lymle's presence gives Tales of Vesperia the edge (no pun intended) in this category. Also, Yuri is slightly cooler than Edge, but Reimi beats all the female characters from ToV. Myruia and Judith are both pretty cool (and have similar physical features), and Baccus and Raven are both sweet.
Better combat system - Star Ocean: The Last Hope. Blindsides are amazing, and when you really level up, you can pull off some sweet combos (not that you can't in Tales of Vesperia, but I really like the rush combos in SO:TLH).
Better music - Hmm, this one's tought as well, but I think I'll give it to Star Ocean: The Last Hope. No real singularly identifiable reason, I just like it better.
So...
Tales of Vesperia - 2
Star Ocean: The Last Hope - 2
Final verdict? Get both! 
"Your grasp of the obvious is inspiring." - Commander Shepard
"I'm Commander Shepard, and this is my favorite store on the Citadel." Commander Shepard
I support JRPGs on the Xbox 360.
Official member of the Xbox 360 Squad
"Nothing can make it moral to destroy the best. One can't be punished for being good. One can't be penalized for ability. If that is right, then we'd better start slaughtering one another, because there isn't any right at all in the world." - Ayn Rand, Atlas Shrugged
