wow this is a good question. it depends on how much experience they gain, what weapons,
armor etc. , and what kind of techs they have. Genis and Rain probably have the most
magic. My favorites are Kratos and Zelos, because they have a bit of everything. Lloyd
obviously has the highest everything (like godlike strenght). U have to work wit Sheena,
but she's good if you can boost her defense with a talisman or somehting. Presea can deal
loads of damage, but it really vulnerable also.

regal seems very strong when you first fight him in the forest, but he isn't as good as
some of the other characters. He can't get as much tetra slash as zelos per say. Although,
he does have healing ability, so he is useful in battle and can deal a lot of damage once
he reaches a higher level and doesn't KO. Also, I agree that EX Skills are important.
Regal has some really good ones.