Faces:
Note: torso seems impossible to me i cant make it symetric

Ha, Ha. Reminds me of my first kit

Make sure you think of what type of head you are going to use since you have two, they won't be easy to fit on the torso. Also try not to go for default shapes, use the pencil tool to sketch out the outlines.

I agree with Ambo. Don't just use the circle tool, try to make the faces according to what most people may look like. Look at a cartoon picture of a human head atomany to get some help maybe. I wouldn't say to go as far as adding ears, but still, the head should be more oval then circle

I like the first one better too. The second guy would have to have a tiny neck:

Finally, you will need more shading on the final one

Also try and work on a more original looking kit. Thinking what makes your kit special from the others.