Personally, my favorite is still Tales of Eternia (fake Tales of Destiny 2 to some :P) My friends ended up going out and buying a multi-tap to play 4-player mode through that game one summer. Totally awesome. Even though the anime was totally throwaway non-canon, it was fun in its own insipid way.
Next on my list would either be Tales of Phantasia or Symphonia. I seem to be leaning more towards ToP lately since I'm hopelessly stuck in ToS. It also loses a few points for mucking up the summon system, making some characters a bit more awkward to use, making multiplayer wonky with the camera, Regal AND Kratos (:P). Mind you it gets bonus points for axe-wielding loli, Presea ftw! Still a very good game, but…not everything that I hoped for.
I haven't played TotA yet, since I lack a PS2, but it seems to be totally awesome.
Still being the avid fan of the "Tales of" series, I'll definitely watch the OVAs. Disappointing that it's all about Sylvarant though...