I recently read an article on this very same topic and, while I enjoyed reading it, I found that I disagreed with several of the author's choices. The listed fighters had good chins, sure, but several of them haven't really had their chins tested. So, this is my take on the matter.
MMA is an ever diversifying sport, changing almost day by day, and fans are starting to learn to respect all the different elements of the sport (In recent fights I've heard fans boo when the ref calls for a stand-up; something that would never have happened a few short years ago). However, there's no denying that the one thing fans love to see more than anything is an all out stand up war. They'll go crazy for the two fighters willing to stand in the center of the cage and bang. But if you're going to be that kind of fighter, you best be sure that you can throw a good punch and take an even better one.