Top one -
I don't think the upper body needs more muscle. The legs are very skinny, but that could be a stylistic thing and doesn't look bad to me. I think his right foot, the one in the back, shouldn't be pointing forward. It's basically impossible to lean that far forward on your foot with it still pointing forward. Instead, try pointing it toward the viewer.

Middle one -
I generally don't go for solid black outlines all the way around things, but if you're going to do that then there's 6 spots (8 pixels total) that suddenly lose the outline for no reason. I would suggest your outline be a darker shade of whatever is the main color for that section. For example, the red jacket could have a dark red outline (like what you did on the scarf of the top one) and the grey pants could have a charcoal grey outline. Again I feel like the back foot should point more toward the viewer instead of both feet being in the same direction, even though it doesn't have the same issue with the lean.

Bottom one -
I think I like this one the most of the three, but that's just personal preference. Try darkening the shirt just a little, because to me the light grey of the headphone cord gets lost a bit in his shirt.

Edited by tanuki - 19 February 2011 at 9:54pm