Yay, summons and the pretties they bring!

My favorite Chocobo is the choco/mog from VII. It was just so cute.
VI's Ramuh, less for his use in battle and more for the character... I love his sprite, sitting there with that most excellent beard.
Shiva from X, because of that amazing character design. The hair! The pretty blue-ness! And especially the animation of her dropping her shawl.
Ifrit from V, I love the attack he dishes out. Hot stuff.
IV's Leviathan, for his position in the world of summons. That is one of my favorite battles, timing the wave is fun.
VII's Odin. "I dont wanna fight this random battle." *summon Odin* Yay!
IV's Bahamut, cause he just kicked so much ass. I loved the flare, and fighting him was a pain in the arse, especially if you dont go the reflect route.

Slyph (IV)! Mostly useless, but pretty!

Imp (IV), because again it was useless, but finding it for the first time was amazing. I was still young and this was a while before faqs.

Magus Sisters (X), because of the IV reference. No really, that's the only reason.

I really liked X's version because of the control aspect and the Aeon staying for more than one turn. I really don't use summons much, save to see their animations. I'm impatient.