True stainless product is priced over the top if you can find it. Stainless is of course used on boats and many things submerged in water.
The galvanized treatment used on screw products seems to be superior to galvanization on nails.
Regardless of your choice, there is a world of difference in galvanized products.
All types of galvanization will eventually rust. Sealing and painting over the galv will give additional protection. The hot-dipped galvanization is usually the best. Electro-plate galv will only last a few years before it starts to rust.
American made Buildex (brand) has an excellent reputation in treated lumber with their screws.
If you don't have time to do it right the first time, when will you have time to do it over?