Most people arrive at this question expecting the answer to be a number. It is not. The caliber you can shoot well beats the caliber that sounds better, every time, and for most first-time buyers the honest answer is one of two.
Quiet, almost no recoil, and cheap enough to shoot a lot. Nobody is going to tell you it is a defensive round, but it is the fastest way to learn to hold a gun still, and holding the gun still is the whole skill. If you have never shot before, an afternoon with a .22 is worth more than an afternoon of reading.
The default for a reason. Manageable recoil, the widest selection of pistols by a long way, and the cheapest centerfire ammunition to practice with. If you are buying one handgun and you want it to cover defense and practice both, this is the one.
Lives in smaller pistols, which is the point. Less recoil energy than 9mm on paper, but the small light guns it comes in can feel sharper in the hand than a full-size 9mm does. Worth handling both before you decide the smaller one is the gentler one.
Both are fine rounds and neither is where we would start you. The recoil is more abrupt, the ammunition costs more, and the practice you skip because of either one costs you more than the caliber gains you.
Roughly from mildest to stoutest. Recoil here is what it feels like in a typical gun for that round; a light gun makes any of them sharper.
| Caliber | Recoil | Practice ammo | Usually bought for |
|---|---|---|---|
| .22 LR | Barely any | Cheapest there is | Learning, plinking, small game |
| .380 ACP | Light on paper, snappy in small pistols | More than 9mm | Pocket carry |
| 9mm | Mild | Cheapest centerfire | Carry, home defense, practice |
| .38 Special | Mild in a steel revolver, sharp in a light one | Middle | Revolvers |
| .40 S&W | Snappy | Middle | Duty-size pistols |
| .45 ACP | A slower, heavier push | Higher | Full-size pistols |
| 10mm | Stout | Higher | Hunting and woods carry |
| .357 Magnum | Stout, loud | Higher | Revolvers; they also fire .38 Special |
Grip fit and trigger reach, not ballistics. A 9mm that fits your hand will outshoot a .380 that does not, and no chart can tell you which is which. We keep .22 LR, .380, 9mm, .38 Special, .357, .40, 10mm and .45 on the shelf, and the pistols to match. Come put a few in your hand and the question usually answers itself in about ten minutes.