I'd go with the .22 long rifle due to the the availability of cheap ammo. Some of the hotter .22lr ammo is close to the .22mag. I like CCI Stingers, but they are rather costly.

IMHO, in most areas where there are farms or out of the bigger cities, the chances of "finding" .22lr ammo is far greater than finding .22mag ammo should you ever have Scrounge.

Many rural "General" stores carry .22 ammo, but often don't have .22mag ammo.

Get a Ruger 10/22 and several extra factory mags and you won't be unhappy.