I'll second Willis' comments: Brass isn't worth the effort. Nickel Silver track costs only a bit more, but by the time you get it in place the the $$ saved are very minimal indeed in the overall scheme of things. Add to it the near-constant cleaning you will be faced with forever I just don't recommend it at all.
Now, saying that I will confess that I have several turnouts (track switches) that are brass, but these are ones buried deep in yards and never see an engine run over them so surface corrosion isn't an issue. It was a case of using what I had available in a manner that wouldn't be an issue.
But if I were to actually go out and BUY one, even for this use, I would go with NS and not worry about it if I re-used it in a more exacting location later.