Moombas - mostly because they left me so curious about their entire history, society (or whatever) etc. when I saw them. They seemed so unique and interesting to me! Moogles are cool and all, as are cactuars, but Moombas to me are more appealing as they seem less kiddy... Moogles and Cactuars are just too darn cute to be taken seriously in a game, at least for me.

Chocobos still are my favourite animal, overall, though.