What follows is the text of an answer that I've given to this question before:
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I've spent time in both the army and the marines; the army is the better choice.
Here is why I believe that the army is the better choice (in no particular order):
1. The army has more MOSes (Military Occupational Specialties) than the marines to include more high-tech MOSes.
2. 90% of all of the special operations forces (SOF) of all four branches of the armed forces are in the army. This includes Rangers, Delta Force, Special Forces (which the ignorant refer to as "the green berets"), Civil Affairs, Psychological Operations and Special Operations Aviation. This does *not* include units like the 82nd Airborne Division or the 173rd Airborne Brigade Combat Team.
3. The army has far more places to be stationed outside of the continental United States than the marines do to include Germany, Italy, Korea, Panama, Alaska and Hawaii. Other than Iraq and Afghanistan, which will end eventually, the only place that the marines have a significant number of troops is Okinawa. The japanese *hate* the marines there because, frankly, so many of them are so badly behaved.
4. If your goal is to experience combat the army has far more troops in both Iraq and Afghanistan (and has taken far more casualites). Despite all this "first to fight" nonsense that the marines constantly spout the army has always had the main ground combat mission. In all of America's wars up to WWII the marines were largely conspicuous by their absence.
5. The army is better funded and the quality of life is generally better.
6. I'm not sure but I think that the army has the best college benefits of all four branches of the service.
7. I speak from experience: the marines harass their troops--needlessly--more so than any other branch of the service. Its like they all have a broomstick jammed up their rectum.
8. Its my understanding that promotions come faster in the army due to how they're structured.
An interesting fact: in its 234 year history the U.S. Army has conducted more amphibious assaults than the marines have. (The marines take pains to *not* advertise that fact). June 6th, 1944, the allied invasion of France was the largest amphibious assault in history.
The marines have a better looking uniform.
Again, I have spent time in both the army and the marines. I know what I'm talking about.