I have no idea what's the top one. The second one was hard too tell. It looks flat. Don't blur the barrel. Your next needs to give up the blur. The last two are better, but you need a focal point. You also use "dissolve" or the noise effect too much. Save that for when you get better at signature. You can make signatures better without having to use all those messy effects. If you use them too abundantly, you'll end up with trash signatures. If you need further help in creating signatures, then I suggest you click "Signature School" in my signature. There are plenty of people there willing to teach you how to use GIMP and all of it's effects.
Well as helpful as your post was Frag, I wouldn't be taking advice from someone with a just as crappy sig... Honestly, to the OP, I think they are all pretty bad. You need to follow some tutorials, just google them. Don't try taking a tut from Frag over here. I remember a site called www.vunkysearch.net that had some really cool tutorials, though I haven't been there in a while.
Site is down. Of course, I wasn't saying I was giving the tutorial. I said there are plenty of PEOPLE there who give help. Especially ones with great skill that pass my own. Now please don't insult my work unless I request it. You'll get banned off this site fast. Oh yea... Spoiler Topaz *****
I can tell you're new to GIMP I'm new too but I've stuck with it for a month or so and I'm getting pretty good. If you want any help just PM me.