I started my modest gun collection after becoming a city police officer in the 1970's...So, .38/.357 by far. I like my autos and really like some of them but my revolvers are my favorites. That's big surprise considering my participation in this forum, isn't if? Ha!
It's a toss up between .22lr, .38/.357, .45ACP, and .45 Colt. Now if you had asked which one I've owned (at one time or another) the most of, .45ACP by far. In fact, when I decided I should try out a different caliber I went with the .45 Colt first. After ammo started to get a ridiculous price tag I got a .22 revolver, and now I think it's the most fun gun I own.
15 or more .38/357 in hand guns and .22s in long guns and a little of everything else thrown in except for .40 and .357 Sig. No exotic or strange metric cals.