They have the best P.R. people. They're famous for teaching recruits their amazing history and installing their values. They're a smaller branch than the Army, they use older weapons but get the harder missions. They deserve their reputation.
They have been elevated to that status by their own outstanding service record, and the myth has been expanded by the media and popular culture. However in reality all branches have elite units, each with excellent histories and traditions. While rivalry exists among the various branches, and it promotes a sense of esprit-de-corps, we are all a team, each with its own responsibilities. Think of it as a Football team, the QB or RB my get more of the praise but without a combined effort none of us would win.
Because to be a marine, you have to be a lot more than physically strong. You have to put both of your feet forward and pray you land correctly because if not, your DI is gunna beat the snot out of ya. SEMPER FI!
I think is because the training is much harder to pass. Also, like everyone here said they are the first and the last. In any case, I am thankful we have them, and also all the brave men and women out there fighting.