SW 15-22 without a doubt. Mine has well over 5k rounds without a hiccup. I clean my guns after every time I shoot them so I couldn't give you a good idea on how it runs dirty. I know I put 2 bulk Federal 550 packs through it last Easter and the only time it didn't go bang was when it was a faulty round. Great gun.
Said that they had way too many quality control issues with the company they where using. About half the crap they couldnt sell because it had some sort of problem. So they are coming out with a new upper but for now its on the back burner for their other projects.