I have a Colt M4 Also All the important parts are metal. The Colt accepts all the AR accessories. It's a real Fun gun!
I own a colt m4 carbine .22 with a 2x7 scope on it, i cant stop shooting it, its addicting, and a very nice rifle. no complaints so far, thats what i chose anyway, but I have a friend who owns a 10/22 and he seems to like it quite a bit, and between the mp15 and 10/22, i would choose the ruger and put all the tactical gear on it. i think any route you go you'll have a blast with it, especially if you're new to ar's like i am!