A lot depends upon the situation one is planning for, expecting; along with other factors.
My usual conceal carry is a 9mm, a single stack and compact size which I can tuck inside waistband and not show much if any imprint. I expect I may need to double tap in some cases. Also usually have a spare mag or two.
My Glock, which is more a challenge for conceal carry - need a shirt/jacket/vest that covers over - I got in .40 cal. Years ago and IIRC, many LEO used such then. I'm very pleased with it on the range for accuracy, penetration, and ease of use.
I also have a .357/.38 Special which is a six shot revolver, but with a 6 1/4" barrel is a large frame and I need either a shoulder or side of leg holster. It is a joy to shoot despite size and weight of the pistol itself. This is the one I keep "under the bed" for home defense(intruder) use. First couple rounds are frangible.