Odin because he's just cool, and has my favorite summon animation out of any of the GFs. (Although it did get annoying when you'd be trying to Mug an enemy or something only to have him come out and kill them off before you got a chance...) Bahamut, because he's my favorite out of the recurring FF summons. And finally, I have to love Pheonix, because I had my ass saved by that thing when I was fighting Ultima Weapon.