In case I didn't make it clear, Phantasia is my favorite game in the series. Second is Vesperia, third is either Eternia, Abyss, or Xillia. Those are my top five. Those five games are why I'm a Tales Of fan, pretty much (although I haven't quite finished Xillia). Symphonia and Legendia are... okay. They each have their strengths and weaknesses. I liked Legendia's characters and their development in the second half of the game, but JAYZUS having to replay so many dungeons and having such unforgiving event flagging.... that's rough.
Symphonia does a lot of things very well, but oh man is it rote. Everything in it seemed like a recycled part from Eternia or Phantasia, and none of the characters really did it for me. Maybe I was in a weird zeitgeist, but I always felt that it was so popular because the GameCube was starved for RPGs. I don't even think it was the best RPG for the GameCube that came out in 2004.
Tales of Destiny for the PS1 is my least-favorite game in the series. The characters don't seem that bad, but the combat was so slow and the dungeon crawls so unimpressive that I couldn't even finish it. I've heard that the PS2, PSP, and second PS2 remakes are good, but I haven't had the opportunity to play them. All I know is the crappy PS1 game.
Tales of Innocence. Man. That game sure loves item hunts. I'll go back to that game eventually, when I have thirty hours and feel like doing random battles in soulless dungeons for hours and hours.