I'd have to give it to the .22, rifle or handgun doesn't matter. I know it's not very high on the "cool" factor, but the simple fact is that it's the only round that the average joe can afford to shoot all day long.
The bigger calibers are to me like serious tools, used for hunting, military or competition. The .22 is more like a fun toy, no real serious purpose behind it, just fun.
A close second would be a 12ga shotgun. Just because I love shooting skeet, trap, or sporting clays. Sporting clays is a lot of fun I think.
Blasting jackrabbits or prairie dogs with a 22/250 is lots of fun to.