I'm not a fan of any TBH but the first Yoda one has good composition, just way over contrasted (and I like contrasty images).
Read a few tuts and keep at it though, for a beginner you ain't lookin half bad.
I think the first two are kinda cool, but you gotta blend the renders more. IMO, with your scanlines/patterns, try to keep the opacity on them at a lower level.
For example, on my current sig my scanlines on the bottom left are set at 40% and I've also erased parts of it.
EDIT: Also try a simple 1 pixel border around some of your sigs.New layer> CTRL +A >EDIT>STROKE
Then make a 1 pixel border of an appropriate colour. Remember too if you have a light border on a forum with a light skin, it'll be harder to see. You can also give your entire sig a drop shadow effect so it "floats" so to speak, but that's another story.