Get something you can comfortably , but also take a look at lethality of ammo too , not all bullets are created equal, and it goes something like 44>357>10mm>45>40>9mm>380>32>25>22.
Plenty of bad guys have taken dozens of rounds of 9mm and not died, so I'd suggest you get proficient with whatever you own before you start to carry a firearm. Plenty of people have died trying to defend themselves due to a lack of training/skill, so when you get something , PRACTICE WITH IT. I'm talking at least 5,000 rounds through it, and consider a tactical pistol course.