Im not too sure on the history of these types of thread. From what I hear there are a lot. And there is an official thread at the top Even though jumping in there as a noob daying " My favorite member is Axel" Will get you flames up the... well you know.
Anyhow, my favorite would be The Enigmatic man, or I just call him Enigma.
Among the ones shown it was Zexion until I found out his powers sucked and he died like a wuss. Now its Axel or Xaldin.