5 rules of a gun fight:
1) Gun beats no gun
This means that the gun you left home because is was too big or going to “print” or what ever reason, is the same as no gun. Guns which malfunction, wont feed right or you don’t know how to clear are clubs, i.e. no gun
2) hit beats a miss
A .22 that hits is worth a whole lot more than the .44 mag that misses. Buy a gun that you can control and hit your target
3) fast beats slow
Usually the one that shoots first, wins. So regardless of the gun you carry, make sure you can get it into the gun fight rapidly.
4) big beats small
Given the three rules above, go for the biggest caliber that meets all three criteria.
5) many beats one
If it is worth shooting once, shoot twice. Two bullet holes bleed faster than one. Take this into consideration and given the prior 4 rules, choose the gun with the most ammunition capacity.