The Fourth Head: I kinda like it but its way to simple, add some detail. 5/10
The Third Head: Same as ^^^^^^^^^ 4/10
Also why are the 3rd and 4th so unclean? There's white dots everywhere and theres jagged lines.
They seem to look alright, pretty simple though. Unless your going for the catoony simple look. If not I would recomend more detail, depth and a few more shapes instead of the squarish looking in most of them, if you get my point. Other than that they are pretty good for a beginner.
Life is like Basketball. Aim, Concentrate, Balance and Following through. That's all you ever need to accomplish your goals.