I know there will be a lot of differing opinions, but what's your favorite? Not for a particular purpose, just your all around favorite.
For me it's a toss-up between 357 Magnum, and 44 Magnum. Both are dual chamberings, both are powerful; and, with the proper training, you can learn to shoot a 357 Magnum, both, quickly and accurately.
If speed (rate-of-fire) isn't all that important to you, then, you can still learn how to shoot a 44 Magnum with outstanding accuracy and at considerable distance; but, from within my own personal experience, I'm going to say that genuinely shooting a 44 Magnum at typical (and, sometimes, necessary), 'combat speed' just ain't ever going to happen; and, especially, not if you want to remain accurate and do something like, 'shoot for group' which is a very necessary CQB pistol shooting skill!