I have brass on my MT and SS on my SS pot. I bought the SS for my pot because my pot was SS..real scientific huh
They both work the same. Save your money and go with brass.
If the lead in brass is a concern just soak it in a solution of vinegar and hydrogen peroxide for a few minutes. There should be a thread on this site explaining how.
there is no way to justify the SS in terms of $ for a homebrewer it just looks better than a tarnished brass fitting or valve IMHO.
My brass ball-valve cracked this winter, I brew outside and I think a little water froze inside. I will be switching to stainless for this reason, though brass shouldn't have cracked either.