Depends also on how formal you want to be. For my wedding most of the invitations were just the first and last name, short first name if it applied (Matt instead of Matthew, for example). For a few people though, we did use the full title. I'd say it depends on whom you're inviting. Someone who you know professionally but don't really hang with (but have a great deal of respect for and that's why you're inviting them, e.g. your OCS DI), or the skipper (someone well above you), you should make that as formal as possible. For your buddies who happen to be O-1 to O-3 I'd just go with first and last name. I'm not a very formal person though.
How formal is your wedding to be?