Keep in mind that this is a freindly disscussion. We dont need to fight amongst ourselves since we're all fans. Just because one person thinks less of the character you choose, doesnt mean that it's canon.
Personly, this was one of the toughest questions. I love Alys at a personal level, but she didn't have the payload of techniques and skills to compete against some of the other characters in the games. Then I thought about Chaz: He can learn Megid, Crosscut, REVER, etc.. And he weilds Elsydeon, but he's not the only person that learn Megid or to use Elsydeon. While he's tough, I had to move on.
Wren: Wren is tough as nails. Surviving through two games is no small task. Packing an array of heavy hitting skills, a self healing skill, the ability to weild the games every powerful guns, the fact that he's resistant to some of the heavier hitting baddies in PSIV, and the ability to heal as he walks make Wren a very strong canidate for the best of the best.
Rune: Though you have to drop him with sheilds, Rune is argueably one of the strongest characters in the game. You dont even need to relay on his TP to get some of the strongest spells in the game. I found myself turning to NaWat only when his God-like skills like Efess and Leagon were depleated. With techs like Rever, NaWat, NaGra, and Arrows, Rune is a one man tank!
So... Here are my ratings.
Rune: 10.0
Wren: 9.99
Chaz: 9.9
Rune wins!!!