Okay, this could be an incendiary topic, but I'm looking at it from the proved events in war and occupations.

WWII: US Army tended to follow the Marines after assaults on the Pacific Islands, and generally didn't do as well as the Marines. Europe etc is irrelevant as the Marines never fought there, but I'd be inclined to think that on the basis of Marine performance in the Pacific the Marines would have done better than the US Army (and any other Allied army) in large scale seaborne landings in the Mediterranean and D Day.

Korea: Chosin Reservoir. Marines fought out in good order. US Army sometimes didn't, and sometimes deplorably so.

Vietnam: Marine held areas performed better on counter-insurgency and other criteria than blunt and aggressive Army operations.

Iraq: Ditto

I'm happy to be corrected, but during WWII and I think at least until Vietnam, and possibly Iraq, we're not comparing apples with apples as the Marines didn't deploy reserve units while the Army did, with disastrous results involving ill-trained and poorly led troops from Buna in WWII right through to Abu Ghraib in Iraq.

I'd be inclined to the view that the Marines imbue their troops with a greater espirit de corps than the Army and from grunt to general have a more innovative approach to war and occupation than their somewhat more bureaucratic and less inspired Army counterparts.