Don't get me wrong, the original AR18 rocks, but it is outdated in the sense that it doesn't come with quad rails, isn't modular like an AR15, because it never caught on and wasn't enhanced and developed like the AR15. The polymer lower of a 180B just doesn't do it for me.
For me, the xcr is an improvement on the AR15, being piston operated, and quick change barrels (and calibers). sure you can change the caliber of an AR, but you need a whole different upper to do it in a timely manner.
The ar180B in my eyes falls below way below any other 5.56 gun, save the mini14. (but it is still non restricted and a black rifle, that is a big + as well)