So I'd have to say the boss I got the most satisfaction out of killing would have to be Seymour Flux, because he killed the Ronsos.
And the Chocobo Eater was fun too, because the first time I played the game, he pushed me over the edge, and the second time, I opened up a can o' whoop-a$$ on 'em!
The chocobo eater killed me that first time. I got soooo pissed off.