Oh ho ho ho! I f*cking LOVE Tales openings! Easily some of the best parts of the entire experience.
I was a big fan of the Japanese opening of Symphonia once that I heard it, same for Abyss. Vesperia made me realize how good the intro could be in English (In fact, I think is much better in English). Also, despite that I thought that both Xillia and Zestiria were underwhelming games, I must admit that they have pretty damn kickass opening themes. Eternia is one of the best in the old-school category. Innocense's is pretty unique and cool. Graces and Hearts' are fine. Rebirth and Legendia's are pretty boring.
I would say that Vesperia is my overall favorite because of how well it was translated and improved.