Mine because it shows my AMAZING artistic ability!!!!!!! ...But, seriously, probably Peaugh or Maximus Prime.
Vangelus' always made and still makes me laugh, even the new one. I kinda liked my old Avatar, which is the small D-con logo with explosion in my sig, not the best, though, and I didn't like how it looked too much like Super_Megatron's. I don't dislike the one I have now, but it's more or less a placeholder till I find something solid. Actually, I really like Super_Megatron's.
Oh oh the thread baby wins it, the avatar of the baby GIF. That was in that crazy thread. You guys know which one I mean? I think a mod uses it.