A lot of it depends on hand size and how you're planning to conceal it.
Pick a caliber and model you'll take with you and not leave at home.
I have a 9mm and a .40 in my "ready" bag. When i leave i reach in the bag and what ever i come out with is what i carry at that time. Both fit my holsters the same.
" If it feels good shoot it"
Happy shootin'