The Smith has a really nice trigger, it's easy to disassemble, and the bolt area is open on both sides so it's easy to tell whether the action is clear from a distance. It's designed such that the barrel can be easily replaced without gunsmithing, although few 22A shooters seem to attempt this, presumably because the barrels are supposedly quite expensive. Finally, it has a ready-mounted scope rail out of the box; only a few MkIII variants come with one pre-installed, and it was not included with a few models the last time I checked, although it's been a while.
The main disadvantages of the Smith are the large and bulbous grip, a few cheap touches, fair-to-middling fit and finish on the cheaper versions (at least the ones I've examined), and a peculiar mag release button that's notoriously unkind to shooters with long fingernails. The plastic recoil buffer requires replacement every few thousand rounds; replacements are quite cheap, but some people seem to dislike this on principle. Finally, it has relatively little aftermarket support compared to the Ruger.
FWIW I went to a show a while back with the intention of buying a 22A, but came home with a Ruger MkII. Although both work well for punching holes very close together on distant pieces of paper, I ultimately bought the Ruger because it has more of a "Real Gun" feel to it.
"Smokey, this is not 'Nam. This is bowling. There are rules... MARK IT ZERO!!" - Walter Sobchak