I wont comment on the last two, they're not my style.
The first one is awesome! Great depth! Great lighting effect, nice colors and background! good flow excellent sig :3
The second one ; Good colors, I think those blue circles/bubbles w/e is beautiful!
The nick is a bit stuck in the middle of there, I think this sig would be great without a nick ^^.
I see there is a bit of flow coming out from Joey, but its tiny so there isnt a big flow in the sig hmmm.. good job again ^^
Third One : A bit empty, bright.. nick is fine but not too good... Nice flow ^^.
You've pretty good sig's.
I would like to see a tutorial about the first one ^^