New Smith 642's/442's are +P rated and fine with +P ammo (I'd stay away from so-called +p+ though in them). For defensive rounds, I'd recommend the Cor-Bon DPX (or Glazer Silver if you're worried about overpenetration) and the buffalo-Bore 158 Gr Lead SWC Hollow point.:
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They also have a standard pressure short barrel load as well--you could shoot both and see which is best controllable for you. I alternate the DPX and Buffalo bore in my Smith new model 40.
As far as the snubby/non snubby thing, you need a gun that you'll carry. Snubbies are "expert" guns -- they take practice to score acceptable hits at longer ranges--this isn't due to inaccuracy but to a short sight radius and rudimentary sights. If it comes down to the snubby on your person vice the large frame revolver in the car, you want the snubby on your person (first rule of gunfighting: have a gun).