I have always been partial to cosplaying as a security officer because if sparks up more conversations (at least with those who get the joke) almost everyone who talked to me said something like "I cant believe you're still alive" or "don't die before comicon ends" and I really like that.
A couple of years ago, I went to an event wearin' my blue DS9 uniform, and most of the comments were about bein' lucky I wasn't in red.