Smith & Wesson Model 327 TRR8 .357 Revolver

Why? Well, despite what most people believe, the revolver is an excellent tactical weapon alternative to a semi-auto. Ammo capacity comes up often as the argument for semi-autos. But current revolvers hold 8 rounds, which is more than enough when you consider that the average rounds fired in an encounter is under 5 rounds. With moon-clips, reloads can be just as fast or faster than magazines (see Jerry Miculek).
Also, revolvers are also more reliable, period. They are simpler mechanisms, with fewer things to go wrong. They are safer, having a heavier double-action pull to keep finger clenching from battle tension from firing an unfortunate round. Sure, it is slower (if you are untrained), but that can be better too, making you aim each shot rather than spraying and praying. Being calm (relatively) and aiming is much more effective in a fight than just spanking the trigger.
Revolvers also allow you to carry a higher power round more comfortably than a semi-auto. When going up against body armor or opponents in cover, being able to employ a .41 or .44 magnum with hunting loads can give you a great advantage.