I went with the 15-22, since it was easier for me to find a place to shoot 22. All my research lead me to the 15-22. It has the same operating functions as a full size AR (except the forward assist). Built it into a SBR, TRS-25 red dot, added a suppressor, and it is my first pick when heading out to the range. I enjoyed that for a while, and then went ahead and I am in the process of building a 5.56 AR.