Everything I read says .357 magnum is more powerful than .45 ACP, on a shot-for-shot basis. If you are limited to 2-3 bullets then having more power in each of them is going to be more important than the maximum potential damage from a full magazine. Also more flexible: almost any revolver that can chamber .357 magnum is also going to be able to fire .38 special, and you can get snake shot for 357 magnum.