Final Fantasy XIII for both. Why? It's the only one I got to play. I really enjoyed it, but I have to admit it had some... flaws. I'm sure I would have enjoyed some others more but I never got to play them (mainly due to lack of time, and other games interesting me more).

Does Fire Emblem Radiant Dawn count? If it does, that's one of my personal favs.

Aside from that, I enjoyed Tales of Symphonia: Dawn of the New World, Tales of Graces F, Xenoblade Chronicles, Eternal Sonata, and the World Ends With You.

Worst one though? Final Fantasy XIII, grumble grumble.

Xenoblade would be the best for me (I'd say it's actually my favorite game overall), followed by Kingdom Hearts Birth by Sleep and The World Ends with you. Most disappointing for me would easily be Tales of Xillia 1 and 2, imo those games are mediocre at best, with their worst aspects being their environments (and personally I hated their art style), and in the case of Xillia 2, both the environments and the debt system.

Edit: sorry for the double post

Best: xenoblade chronicles
worst: FFXIII

I actually found the question pretty tough...

Best:

Lost Odyssey (360) - This game gave me a lot of feels.

Worse:

White Knight Chronicles (PS3) - The characters were just boring. This is the only game that I enjoyed grinding than forwarding the story. lol!

I think you're probably one of the very few people that like that one xD

I guess the weakest I played was Glory of Heracles. It wasn't bad though, just kind of average.

Dark Souls

Xenoblade and NiNoKuni. Soulsgames don´t count imo