Depends on the gun. Slim single stack for CCW? The 9mm is king, but a full size for home defense... yeah, maybe .40. Lately tho, I've concluded that if you reload, then for a full size handgun, skip the .40 and go straight to 10mm. More power with the full power loads, but still capable with the light 10mm loads.
I can't say I regret buying a Glock 35 brand new a few years ago, but if I had known at the time I was going to get into reloading, I would have gotten the Glock 40 MOS instead. I bought a 9mm barrel for the G35, nice to have the option of reliably shooting 9mm in it, don't have that capability with the 10mm Glocks.
9mm aint my king.
I have a Shield 40 that I carry in weak hand front pocket as a 2nd option to the 40/45/10mm that I've got on my belt.
I have a Glock 35 and have carried it quite a bit, but my 20SF (or 21SF) gets carried more.