I find that when considering a carry gun, it is always good to remember the 5 rules of a gun fight:
1) gun beats no gun
That means that the gun you left behind because it was too big, too hard to shoot, too costly to feed = no gun
2) a hit beats a miss
The .22 that hits beats the .44 magnum hand cannon that cant hit the broad side of a barn
3) fast beats slow
Fast as in how fast you can get the gun into the fight. Often, he who shoots first, shoots last
4) big holes beat little holes
Bigger holes bleed out faster so carry that largest caliber that can still meet rules 1 through 3
5) two holes beat one hole
If it is worth shooting once, it is worth shooting twice. Keep this in mind when you are comparing the number of rounds available to you.