1. I like it, but it's a tad too dark IMO
2. Nice, but eh maybe a little plain and the render is slightly LQ...
3.I like it, but the render and the background blends in a ay I'm quit sure it's not supposed to (part of the render becomes more or less invisible).
4.Render sort of appears to be floating on top of a background. The background in itself is nice, although it lacks a colour spectrum,
All in all fairly good submissions. My vote goes to number 1 though.