Don't much care for AR-15 and other M-16 derivatives. The .223 round it's built around it too easily defeated by modern, lightweight body armor. In my military career (30 years and counting in USAF) it's also been my experience that they malfunction WAAAAAAAY too much.
I used to have a very nice Browning Hi-Power (P-35). Great gun. But even it's 9mm round is too small. I'd like to get another one in the .40 S&W.