I would recommend the S&W, but $700 is on the high end for a sport. The last DPMS that I saw had an out of spec lower, with a super tight mag well. I was watching a guy try to shoot it and thought it wasn't cycling a round when in actuality the mag wasn't fully inserted, but the mag well was so tight that a fully loaded mag wouldn't drop out.
Or look at a PSA. For $700 you can get an upper with a high quality FN barrel and a lower with better than standard furniture.