I've always hated sigs like that.
The wakka one is cool, despite that wakka picture seeming stretched out a bit. The Hulk one lacks contrast, and just seems kinda dull imo.
You should have tried the effect you used on the hulk sig with the wakka sig.
Also, try and incorporate some borders.

Oh, also, try working on some better text. I love the first one to death and I think that a border and a fullsize wakka would compliment it well. If you need tips, ask.