If you wanna save the meat (and you should) go for head shots. Body shots are often messy, and ruin alot of good meat (and there's not that much there to start with). And, for head shots, almost any .22LR will do the job.
My buddy and I just spent several months trying all kinds of .22LR ammo, in 5 different guns, to find the most accurate loads. They ALL liked standard velocity, 38 or 40 grain loadings the best. Some of the high velocity stuff was OK, but none was as accurate as the standard stuff. The 3 best we found (and this was pretty much for all 5 guns) were:
Wolf Match Target
Winchester T-22
Federal "Classic" Gold Label
So try these for starters. But every .22 seems to like something different, so try out some different ones as well. Some people DO get really good accuracy out of the high velocity ammo.
If you don't have a really good scope, consider buying an inexpensive one.
I was given a Marlin Model 60, with a junk Tasco ".22" scope on it. I replaced it with a Tasco "Pronghorn" ($40) and it now consistently shoots 10 shot, dime sized groups at 50 yards (perfect for head shots on squirrels) using the Wolf Match Target.
I also have a 25N bolt, with a similarly crappy scope (a 2.5x Redfield)...I've not used it much, but think I'm gonna buy a better scope, and see what it'll do. The reason I don't shoot it much, is the model 60 is SO darned accurate, I just love shooting those tiny groups with it. But I suspect the boltgun can be just as accurate.