I think this mostly depends on you, your pistol, and how you plan to use it. Releasing the slide stop with your thumb is probably the fastest method, and in competition and self-defense situations, speed matters. However, from a personal-protection standpoint, what happens if you fail to release the slide stop with your thumb? In competition shooting, you can make up time lost in one stage on the next one. When shooting in self-defense, what you risk losing is your life—not seconds on a shot timer.