screws in my opinion keep things together longer and do not "walk" out on you.
But, to screw is more labor entensive and takes longer and in some cases not even needed. I do find myself using ring shanked nails more and more because they do stay in.
Planks on a deck are a good example where smooth shank nails should NOT be used. Here is where screws or ring shank dry glue nails should be used.