Favorites are nice, and watcher's are really nice. But comments are what its really all about. They let you know you're not out here in the ocean of art alone. Someone has decided its worth talking to you, if for just a bit.
Dangit, didn't see the 'comments' option and voted 'favorites'. Let's just pretend I voted comments.
It takes all of 5 seconds of effort to favorite. Just a bit more to look at the artist's page and watch. But someone has to take a deeper interest beyond dA's equivalent of the 'like button' in order to comment.
Comments are the best. They can give you constructive criticism or simply make your day with some sweet words. It means someone cared enough about your artwork to contribute their own little tidbit. There are the occasional times people tend to post silly, rude, or pointless things but overall, I care most about comments.