As far as the guns that chamber them, I prefer shooting the .45acp, because I own a H&K USP with 12 round mags and that is a LOT of firepower in the palm. Fun!
As far as the actual round is concerned, I will take the .357 mag over ANYTHING. Superior combination of stopping power (that's right-- stopping power is real; it means the effectiveness of the individual projectile in stopping the target), distance, control, economics, variety of guns, etc.
The .357 mag is the mutt's nuts.