I really like the colours of the last one
Also, if you wanna make that transparent one look right, save it as png (but it will only look transparent for people who use internet browsers which support PNG transparency [ie most ones apart from microsoft IE]), or make the background colour black, or make the matte black when you save it, or don't use a matte at all. I wouldn't suggest using the last option, as it can make the sig choppy - I prefer the PNG. I suggest learning some new render blending techniques too - try smudging
