It's not the image quality I'm so worried about as the cutoff at the middle-left; it looks extremely messy. Was there a reason you decided to cut the image off at that point, or was the source image cut of at that point, or what?
In the latter case you could've blended the left edge of the render into the background so it'd fade into the backing instead of just cutting off at a (nearly) flat edge. It'd take some manual work to do this, but I'd say it's very possible even with a single layer.
I prefer the second image to the first and third. My reasoning is thus:
The first image involves filter and/or brush effects that overlay the render. This is fine if the effect is subtle (as it is moreso in the second image), but in this case it looks as though we're seeing the image through a textured fog. There's also too much blur for me.
As for the third image, I always feel that it's better to use contrasting colours as opposed to an entirely consistent colour scheme. If you can't use contrasting colours, use complimentary ones, but always use different colours. The main reason the eyes can stand out on the render is that they contrast with the colour of the skin - and in the third image everything's green, so you miss the details. I often find that it's a matter of drawing attention to the best and/or most attractive parts of an image, and one of the easiest and best ways of doing that is by using contrasting colours.
Anyway, I hope that helps. Glad to see that you're making an effort at improving.