the last one is the best looking.
>.> the head looks wierd. the is very distorted. Warts distored. it doesn't look good at all. the left sides of the sig is the only good looking thing on here.
The Kennedy sig background looks good but he stands out from the background. it doesn't blend. it's like looking at a pop up book. that's how much the stock stands out. try to get some differant colors and blend in the stock more.
Your third one. >.> the background could stand out more, the stock is poorly cut, and it's not good on the eyes.
for your last one, blend it in more and smooth it our more with, Filters>Noise>Reduce Noise. play with the settings.