The only decent one is the varus mechanics, just because you didn't do much on that poor render unlike others.
Either they're blurred, too sharp or absolutely flat. Most are also made from simple brushes and random effects thrown in.
My suggestion to improve is to make clear designs, the less the better.
Pick a render of your liking, pick two to five colors from the render itself and forget about filters.
Always play with your render: try to put something in front of it which works with the background, all your works are composed of a render with background, with some absolute horrifying filters added sometimes ( like #8 and #11).
I'm sorry if i'm being a little too harsh but when i started making sigs i too made them similiar to you and people told mey they liked it, so i kept doing those.
Then as a i got better, i simply understood how insanely bad they were and moved on.
If you're using gimp and you use brushes, you need to play a little with the size: let's say that at 200 size the brush is perfect, at 201 and 199 the brush will be blurred, and it'll be for a few more sizes until being sharp again. So before you use brushes, play with the size a little and check it's not blurred.