I have found that the most important thing that will affect your accuracy is the aim!! Now that is elementary, but it seems that a revolver, being slower to fire, will cause more people to take their time and aim properly. An auto handgun will usually cause people to just shoot faster and their accuracy will drop.
I have both and I have fired equally when I take the time at 25 yards. With my revolver, I am a little more accurate cocking my revolver each time as opposed to using it double action. I think that is due to the shorter pull of the trigger as opposed to double action.
In a matter of personal protection, speed will not make much difference in your aim but a couple of inches, so you will probably be okay with an automatic. If you fire and hit the target the first shot and this miss it the next xxxx times, you are probably better off with the "wheel gun"! The whole point is to HIT THE TARGET!!