I say Hamed by stoppage after suffering a knockdown, in a very entertaining fight. Chacon would have pressured Hamed trying to knock him out, but Naseem's reflexes, speed and power would have been decisive.
Chacon was so strong, durable, and tough, with excellent condition and a will to win. He had the punch to hurt Hamed. He also would have been willing to take a lot to dish his own. BUT, the problem for Chacon is he was way too hittable, which is not a good quality to have against a guy as fast and powerful as Hamed. I don't see this ending well for Chacon.
I fight i would have been pulling 100% for Chacon as Hamed is on the short list of fighters I despise. But like the others have stated he was too easy to hit although he did have the better chin