I applied to USMC and USN at the same time.  Due to the selection process, I was picked by USN first.  My report date to OCS was before the USMC board, so I didn't want to chance it.  I did not have a preference, so that helped drive my decision.  Although sometimes I wonder "what if", I don't regret going USN, it has definitely worked out.  I would say that if you have a great desire to be in a specific branch, focus your efforts on that one.