I absolutely love the G20/21 SF frame.
The wide grip really helps to distribute recoil. The slide lock lever is completely out of the way, and it even sticks out less than on the other frames. The slide is perfectly flush with the frame. (On the 9mm/40SW frames, the edge of the frame sticks out past the slide on the sides, and this is annoying due to my shooting grip). The G20/21 SF frame is just flat and smooth in all the right places. And the top of the slide looks like an aircraft carrier, guiding the way during fast shooting. This frame also has the least grip angle of any of the Glock frames.
And most importantly, it must fit me pretty well. I never pull a shot with this gun, doesn't matter how long it's been. Shotgun hulls at 50 feet? It's on. Beer bottles at 75 yards? Bring it. I am confident on shots I wouldn't even try with my Glock 19. I am more "money" with this gun than a 686 with a 2 lb trigger or a Colt Gold Cup. About the only thing I have shot that has ever compared, in my hands, is the German Sig P220 in single action. (P226/8 is oddly inaccurate for me).
It also doesn't hurt that it's one of two guns that I own that has never, ever had a malfunction. My FNX is still in the running, but it has only seen 1/10th the number of rounds. I might add that I've never had a user-induced malfunction or a neglected maintenance malfunction with it, either, knock on wood.