SS because it looks more like white gold : ) something tells me you started something akin to the aluminum/stainless controversy
Stainless, so you can get a 3 piece ball valve. Way easier to take apart and clean if needed. Plus all stainless does make you look like a baller.
Brass because it's cheaper, and it does the job. You don't need Cadillac everything. Spend your duckets on the things that will Really make a Noticeable difference in your final product.