I'm taking Sheriff Campbell's Defensive pistol class this summer. And I currently have 2 pistols. I'm not quite sure which one I should train with for the class. Glock 19 or the Glock 21. I carry the 19, but I feel pretty comfortable shooting the 21. But I would like to get real good with the 19, since its the one I carry. So how do you choose which one to go with?