If you are going for a gun that will be mainly for metal and looks than go with the classic army.
But if you want utter relaibility and a gun that will always work no mater how you abuse it than go with marui.
Classic army is still a relitavley young company in the airsoft industry. They do make good guns, but they arent the most reliable at times. They are reliable for a while, but you can say that after a few years of service at least one major problem is always encountered. (Ive fixed alot more ICS/CA boxes than I have marui boxes. The only drawback that marui has is that they dont have as much metal on the bodies. But they probably make up for it in terms of reliability. Tokyo Marui has been around for nearly 20 years, and by now they know what they are doing. They have spent the time to engineer their guns to stand up to years worth of wear and tear. I guess you can call them the "workhorse" aegs, because even if thay arent as pretty, they still keep working through thick and thin.