For quantity it's a toss up between .45 Long Colt & .455 Colt/Eley. Having said that, .44 S&W Special is starting to burn up that trail.
The longer I've been playing this game however, the more respect I've gained for a .38 Special with 200gr cast boooolits @ 900'/sec... The equivilant of the old Winchester "super police" loading.... Think about it.
The caliber I've shot the most over the last 10 years? Definately .45 Colt.
There is just something comforting about a 255gr .452-.454 SWC @ 850'/sec.