soft as in silicone? do not ever buy a silicone
soft as in the iskin solo that jeremey sikora just reviewed? maybe
right now, i have: the incase slider, seidio innocase, incipio feather, and my speck candyshell should be coming in soon. im sure you can tell from those examples that i prefer hard cases
if you're looking for a combination of hard and soft, check out the candyshell
i forgot to answer your question..
Pros: good protection from drops, insides of the case wont scratch the phone, provides grip, usually easy to put on
Cons: sometimes too much grip, will attract lint, the silicone may get discolored, some of them cover up the on/off and volume buttons (may be a pro to some)
Pros: usually thin and light, most are easy to install, some have nice rubberized coatings on the outside, easy to access the buttons
Cons: scratches the phone, may have gaps that allow dust to come in between the phone and the case, minimum drop protection (depending on the case)
im sure there are many more pros and cons, but i cant think of them right now.
you may want to check out the first two posts under the "All iPhone Accessories" section
i promise you will never find the perfect case, which is why i have 4 different kinds.
hope you find what you're looking for