I like the consistent speed I can achieve my double-taps using the 9mm.
-If I do my part, the 9mm is a capable round to take down most threats.
45 ACP is a close second, though. For all those meth-junkie silver-back gorillas everyone anticipates encountering in a SD situation. I'm just not as fast with it.
9mm - Overal winner. Cheap, fun and moderate noise/recoil. Easy to shoot fast with good accuracy. If I got into a real firefight, I'd want 9mm for these reasons and for the fairly mild report. And of course, I get to shoot it through a Browning Hi Power.
.357 Mag - My fav Big Bang handgun ammo. Does the water-filled milk jug thing very nicely, I can really tell the difference between .357 and more standard rounds like 9mm and .45 ACP. So many tremendous guns available in this caliber (thinking about adding a 7.5" Ruger Blackhawk to the stable). However, it's fairly expensive and therefore not guilt free like 9mm. I have some .38 Special, but I hardly ever fire them, that's not why I bought this gun! Wouldn't want to be in a firefight (with no hearing protection ) with this round!
7.62x39 - A dirt cheap 30-30 you fire through an "assault" rifle---I'm in!! Of course, .308 and the "assault" rifles it fires through are much better, but expensive for plinking.
7.92 x 57 (8mm Mauser) - The German .30-06 when you get full power rounds. Unleashes big time hurt on targets, lots of fun and dirt cheap surplus ammo, great hunting round also (full power). Big fan of German Mauser rifles.
For a revolver, the .44 Magnum, because I can load .44 Special "+P" all the way up to full magnums. A close second would be the .357 magnum, especially in a revolver that holds 8 rounds.