.22 Hands down. It's easy to shoot well. It's quiet. It's cheap enough that I tend to shoot it a lot, and that leads back to the first reason. Ammo is easily available,small, light, accurate, cheap, and if placed correctly, will kill anything I'm ever likely to run up against. I grew up on a farm, and I've seen full grown steers drop like a sack of sand, due to a single properly placed .22lr on butchering day. Same thing with 350 pound hogs. It's not the weapon of choice for a lot of applications, but I've got to go with it for best "all around". Second place goes to .12ga. After that, it's a toss-up for which .30 calibre round you like best.