From Lazs:
"The most accurate 22's I have ever shot are almost forgotten calibers... the 22 hornet and the 22-250. It is easy to shoot 3" groups at 300 or so yards with the 22-250 and the hornet will have more energy at 100 yards than a 22 long rifle at the muzzle."
This also boils down to the ammo price. The last one to be really cheap is .22 magnum, after that you are in the bottleneck business. A Hornet is cool, slightly more powerful than a .22 magnum, which still is supersonic. Then you have what, 222? Then 223 ? And 22-250, that's one of the fastest bullets of them all. At 250 yards you still have no drop, - but with a fast bullet like that, you better have the ground in the background!
Forgotten caliber????