I think adding "Most Favorited" would create a popularity contest and people would start looking for ways to game the system. I don't think favorites should have metrics associated with them because as soon as metrics are introduced people will try to optimize them.

Now that I know comments can be favorited I plan to bookmark comments that include useful reference information on topics I find interesting. Adding counters for how many times the comment was favorited wouldn't really help me with that use case because I doubt anyone else cares about collecting useful references so my favorites would never make it to the "most favorited" list. I personally don't care if I make it to the list or not but I'm certain some people would care and they would go around and start playing a popularity contest instead of looking for ways to favorite information that would be useful to them.