I like the sound of
Damon more than
Damian, but I'd go with
Damian because
Damon would probably be associated with
Matt Damon by many. It's not that I dislike
Matt Damon or anything. I just wouldn't want people to think that I named my child after him, and I have a feeling that I would get a lot of comments such as "Oh, like
Matt Damon!" I think that would get old.