The Buck Mark does need tools to disassemble for cleaning, but the Ruger Mk III fits together like one of those damn chain puzzles.
The Buck Mark feels better with the wood grips...at least to me it does.
The Buck Mark also has a crisper trigger than the Ruger Mk III, and not so much travel.
You can swap barrels out on the Buck Mark but not the Ruger (at least not legally).
http://www.tacticalsol.com/homefast.htm
Stay away from the SW Model 22A...you won't like it...feels likea kids toy.
Also consider, though it is more expensive, the Ruger Single Six revolver. You can swap cylinders from a .22 LR to a .22 Mag. You can also get it it .17HMR if you feel like adding a bit more punch to your hunting.