When building a deck, always use screws instead of nails for these reasons:
Screws hold better than nails.
Screws are easier to "sink" into the lumber.
Screws don't back out of the deck boards like nails (no more toe grabbers).
It is easier to pay attention to placement with screws than with nails. Using a nail gun, we tend to nail fast rather than correctly.
Be sure to use the proper screws. Gold colored, zinc-plated deck screws are my choice.