FWIW, I really like my 5.56 AR with 18" barrel and rifle gas. Handles better than a 20" barrel while giving a bit more velocity than the typical 16" carbine. The rifle gas gives up nothing in function or reliability and easily handles the addition of a muffler w/o alterations.
I lucked out buying my first AR at my LGS while they were having "Ruger Days", a super sale on Ruger products. The MPR had just been released. I picked my 18 inch up for just over $500. It's been solid.
