My list goes like this:
1. .22 LR
It helps train a shooter for the rest. The place to start in competition shooting, small game hunting etc. Can be used for defense in a pinch.
2. .38 Special.
Easy to load, accurate, easy and fun to shoot. Lots of guns still available including easily-concealed snubnoses.
Not a bad defensive caliber if others are not available, or too powerful to handle.
3. .357 Magnum.
Good hunting and defensive loads are easy to buy or make. Lots of guns available including police turn in bargains. I know a guy who filled both his deer tags with a six-inch Colt Trooper .357 one year. I've hunted for deer with mine, but not gotten a shot. Can use .38 Specials for cheap practice and small game.
4. .41 Magnum.
A bit off the beaten path, but well worth the trip. Accurate, powerful, easy to handload. Smacks bowling pins around well, takes steel plates down with authority. Some of the most beautiful Smith & Wessons are old M57s and M657s.
5. .45ACP.
Just got done loading a couple hundred target .45s for my son The Bullseye Shooter to use in practice. The .45 is one of the easiest handgun rounds to load. When I started loading the .45, years ago, it took just three tries to find an accurate load. (Not true of other handgun rounds).
Lots of smash but easily controlled. I've used the .45 contentedly in 1911s, a 1917 Smith revolver, and several subguns.