Have you seen the Deck Screws that are on the market these days? Epoxy Coated Green, Polymer Coated, Stainless steel with a robertson dive (Square). There are many more choices that just Hot Dipped Zinc and Brass. I put some fence boards that I replaced with some of the Polymer Coated several years ago and they are still as clean as the day I put them up.
I went through that issue a few years ago.....What you use depends on the type of wood....besides the screw corroding...there are issues with wood stain....or basically, that black streak that goes down the side of the wood from the screw.
For the most part, I think brass is ok for most woods though I recall (I think) that it might react with some woods. I know there are a couple of woods that stainless should not be used with....but for the most part, the epoxy coated do real well. I used them on a gate and when I tore the gate apart after 6 years....no evidence of corrorision....or wood staining.
Do an internet search and if you find anything please post it here....I would do it for you but I'm really supposed to be working right now instead of doing this.....
I have a lot of wood around my garden, gazebos, gate posts etc. All are fitted to masonry, or to each other with brass screws. They come apart years later with no problems.
I never have done a deck tho.
That is what I built a deck with 6 yrs ago, still look like they did the day they were put in. Coated screws the coating will sometimes come off when the screw is put in which will cause corrosion or black spots in the wood like someone put a spot of black dye on the screw & it bled off into the wood. This happens with redwood & cedar, using stainless prevents this. I order my screws from Mcfeely's & have been pleased with them. They have different grades of stainless screws & also carry brass or coated if you decide to go that route.
Wow, tons of love for square drive stainless, my local places started carrying torx stainless and reg desk screws, along with builders screws for interior. I wouldn’t go back to square, the torx are good, and the drive slot is easier to engage when driving late numbers of screws, as it can be chamfered.
I hope the OP already has dealt with this as the original posting is 12+ years old. Personally, I like torx but I have no idea what was readily available at what price 12 years ago. Or with supply chain disruptions of this Covid era ..... what is now.
Back in the day, we did not have Stainless Steel screws, Back in the day Zinc was used as a sacrificial anode anode designed to protect other metals from corrosion.
Get up to date, a good grade of stainless will not disappoint you.