Gosh, what a toughy. Let's see here... I pick Rune, Rune, Rune, and... Rune.
Okay, seriously:
1.) Rune Walsh: No explanation needed as the others have pointed out, but what the heck - I have to admit, his Rever, Efess, and Legeon are just.... yeah. Swoon-worthy. Ehe.
2.) Raja: His healing techs are unmatched. And, his skills are pretty sweet - bringing back magic techs for the party members and such. St. Fire is pretty awesome, too.
3.) Wren: If he hits zero and an other party member is still alive, he will automatically come back at the end of a fight. He also has proven to be really reliable in a fight; the damage he inflicts with his guns, and his ability to recharge in battle has been impressive. Also - *barrier has been beyong useful for battle defense.
4.) Myau: He can turn into a big cat... and fly
