I'd have to say either Zalera of Famfrit.
I love the whole angel of death aspect and Famfrit is just strong and very cool looking special attack.

Cuchalain and Chaos. The only one I haven't got is the last one, but I'm assuming I'm gonna like that one the best.

I haven't used Zalera yet, but of the ones I have, that one seems the coolest.

Hashmal is cool

I actually like Zodiark. It took a while to grow on me, but I think it's kind of cuddly.

SUPER MAN ESPER

I kinda like Chaos cuz of his attack and the ability to use a lot of different Magicks but Famfrit represents my Zodiac sign so i like him as well....