I've played Symphonia, Abyss, and Vesparia (in that order).
By in large, Abyss is the best, hands down. Best cast, great voice-acting, fun writing, interesting dungeons, some cool plot twists (some not so good). Unfortunately, fairly bland graphics, longish load times, and probably Sakuraba's most boring soundtrack. However, the cast completely wins out. The game is just FUN. I thought the battle system had the best balance of complexity without being aggravating.
Symphonia has the best dungeons and puzzles, a memorable graphical style, especially great for the GameCube generation. Some great characters, but unfortunately marred by some terrible ones, and some bland dialog (though some great stuff too).
Vesparia is far and away the worst, though. The dungeons, while pretty, aren't fun. Except for the main character and Judy, the rest of the cast ranges from "annoying" to OMFG STFU! Too bad, because it's got a really strong male lead with some interesting personality. But I found the game too damaged to enjoy. Most of the dialog is crap, the story is uninteresting, the battle system is way too random and complex to be fun, and the female lead gets herself on the list of worst female characters in RPGs (if I remember correctly). Honestly, the graphics didn't blow me away either. Some moments do, sure, but at other times, they boosted the contrast so high that it's very difficult to see anything in shadow. The "pretty" graphics just aren't worth the price of everything else. Play Abyss.