I don't have any experience with stainless slides but on my black (blued) guns the finish begins to show signs of holster wear over time. The FS M&P 9 and my Shield show it bad but my G17 seems to hold up a little better. I can't help but think a stainless slide wouldn't really show wear but I could be wrong. I vote stainless!
"The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government." - Thomas Jefferson