Aeso, that's a great sketch. It's got a nice loose/free feeling that's missing from your Illustrator version. Did you "place" it into your illustrator file as a template? I think that would really help add some life to the lines.
I like that overlapping like on his jaw/jowel on the sketch. It has a better flow. Also, the second line defining the bridge of his nose flattens it out too much. The sketch version has a cleaner look.
Also, a better way to get the thicker contour line is to block the whole shape out, do all the lines normally, then add a thicker stroke behind the object. I don't know what version of Illustrator you're using, but if it's CS, you can group all the pieces together and add a stroke to the whole thing and slap it in the back.
Although that's really derailing the thread. :)