its not that hard to get into the rangers assuming you have the mental and physical ability , marine sniper program well the army has aboput 1000 rangers for ever sniper the marine has and trust me a recruiter will not tell you how there are plenty of grunts that never got the chance to be sniper
so if you want a garrentee you do the work the army will make you a ranger
i dont know that you could say that about being a sniper in the marines

either will look good on a resume in the future
niether one will allow you to be a serious weightlifter/bodybuilder on a year-round basis