I really like the .22lr. It is cheep, fun, quite, recoiless and you can become pretty deadly with the round. I do not hunt out side of 50 years with it though. Another plus is, there is tons of ammo types for it.
On the same page, there is alot to be said about the .17HMR, .17M2 and the .22MAG. I still like the .22lr the best because it not much loader then a bbgun, I like to shoot at night. The .17M2 would do the job too, about the same as the .22lr, and the .22lr is still cheeper. I still would not go past 50 yards with either one though.
If noise is not a issue, I would go .22MAG, or .17HMR
Dave.