Marines have an attitude that they are best in the world and look down their noses at the other branches.

Perhaps. It is true that the Marines are a pretty confident bunch. I've experienced the "we're the best" attitude in all the services, though the Army and Air Force people I've met almost seem to adopt this attitude because they are expected to and only take it half seriously.

s there really a compelling reason to choose Combat Arms in Marines over Army?

Not so far, it seems. If all you have to go on is the impressions of a few of us on the BBS, I'd say go to the service you're confortable with. I just wanted to make sure you'd considered all of the options.