I own and carry with both. The comp-tac is a better quality holster, and carries larger guns better (G19 and BHP). I originally tried the AG 2.0 holster for the same guns, and was less than impressed with both. it just didn't fit right, and the molding of the shell made drawing/ holstering difficult. I had to use a heat gun to put a bend in the shell to make it contour to my hip, and to adjust the amount of retention on the gun, and flare at the opening for easier holstering. Comp-Tac has better construction materials and a better design, but you pay for those. I now carry a Kahr in the AG, and am actually pleased with it. I recently had the structured material in the holster break, and when I called them up they sent me a new holster base, no questions asked; great customer service.
In short, Comp-Tac is a better quality, more comfortable/adjustable holster, but at 30-40% the price, AG is decent, with GREAT customer service.