I have the carbine flat top AR-10. During breakin i had a few jams, and thats normal, but after a few hundred rounds through it, its smooth and troubble free. The accuracy is impressive.
I have lots of converted 20 rounders as well as 1 10 rounder and all work flawlessly. I would highly recommend the AR-10, especially for its ergonomics and balance.
The only problem with my AR-10 is that i'm in CA, wont register, and had to smuggle it into a free state. No i can only shoot it once a year when I drive accross 4 states to play with it. =(