Pressure-treated wood is disease and rot resistant. Using galvanized screws or nails does not affect the pressure-treated lumber's effectiveness.
Using nails or screws in the construction of a deck is the personal choice of the contractor--the benefits of nails or screws are slightly different. Galvanized nails could lift from the wood, whereas galvanized screws are less likely to lift and require attention in later years.
Both nails and screws must be made of galvanized metal and designed for use with pressure-treated wood. Nails and screws are different in that a nail is installed with a downward force into the wood and screws are turned in manner that ensures longer-lasting stability.
Preventing pressure-treated boards from overshrinkage is easily achieved by applying a preservative to slow the drying process of the wood. The preservative also protects the tops of the screws or nail heads, making it less likely they will lift from the wood.
The cost for galvanized nails or screws to use on your deck is about the same. If using a nail gun, securing your deck boards is a quick task. Using screws can take more time and effort during installation.