Actually, I would definitely use a nailer for siding: there's less chance of cracking than nailing manually, and if you set the pressure and depth properly, you get a perfect nail every time.
Don't use a regular nailer. There are special siding nailers that use a thinner shank nail. I bought the Bostitch version and it works well. Galvanized nails wouild be standard, but its worth looking around on the internet for stainless nails as they will definitely avoid future rust stains.