I like to think of Tales of Symphonia as my first real JRPG apart from Pokemon. While it took about 20 hours for me to even start to appreciate it, by that point I'd fallen in love with the world, the characters, the visuals, and the music. The gameplay was also fantastic.
Vesperia is the only other one I've finished. It's better than Symphonia in some respects; combat has been refined, the visuals are a solid evolution of what came before, and most interestingly, the characters are far more relatable. Yuri in particular goes down as quite possibly my favorite protagonist in the history of RPGs. Rita and Raven are also well-written. I've never minded tropes, so Estelle, the naive noble, and Karol, the resident Ash Ketchum, never bothered me, though I understand many people had problems with them.
It's been some 10 years since I last played Symphonia, so I'm not sure how Vesperia stacks up relative to that one. I do recall that Symphonia had a better story, but I like Vesperia's characters more.
I've played Abyss and Phantasia but finished neither. Phantasia I should certainly get around to finishing. As for Abyss, I found the protagonist insufferable. I might give it another go, but the characters all failed to connect with me.
I'm not sure I've played enough to call myself a fan of the series, but Vesperia, Symphonia, and Phantasia are all solid games.