(first my backround. 6 years USMC. 6 years USAF 12 total active service. I enlisted in the Marines when I was 18 and had a tech job working on RADAR. Since then I've worked with all branches of services quite extensivly)Good or bad here's some of the differences I've noticed:
USMC
Smaller service. ONly about 180K+ This can be good or bad. Good in the fact that you aren't allways just another number, bad in the fact that you have a smaller budget and the Marines are well known for doing more with less.
True every Marine a rifleman. I worked on RADAR but did alot of ground ops as we were allways tasked with providing our own perimeter security. The Marines have good educational benifits but the Army has alot more. (more on that later)
ARMY
First off they've lowered their standards for enlistment. While not all soldiers are douchbags you are going to find alot more as of late. You also make rank alot faster in the Army. The army has more educational programs such the army advantage fund and the latest one of garunteed loans/grants for small business when you get out. They also have better retention bonuses.
The Army is a HUGE service though. A bigger service usually means more BS rules and regs. It also means things are usually less personalized (take that how you want it) IE the difference between working for a big corporation or a small business.
With all things considered the Marines are stronger on tradition. When it comes to dropping the panties of ladies nothing beats these: