Best to follow the hanger manufacturer's directions. Most I've used require 16d galvanized nails in diagonally-driven locations and 9d 1 1/2" joist hanger nails where driven across the width of the joist. I have used exterior grade screws for these and I believe they will hold better, but you must be sure they are not brittle like sheet-rock screws as those will snap under a load as they are too hard. Also be sure the ledger band is attached to the house with lags or carriage bolts every 24" or less as many decks and porches have fallen when nails pulled out.

A palm nailer can make working in the tight spots a lot easier. For one or two jobs a cheap one will do fine. Once you do these with a palm nailer, you'll never go back to the smashed fingers of nailing hangers in with a hammer!