Unless I intend on carrying a specific gun, I always choose the Blued model over the Stainless. In general I find Blued guns to be a bit smoother, less reflective if shot in bright sunlight, and I just like the way they look. The only Stainless guns I own are my dedicated carry guns - - - M60-7, M65, M63. The rest are all Blued with a few "Cowboy Guns" in Nickel for good measure.
That said, if you intend on taking your gun out often and exposing it to the weather, Stainless (M686) is the way to go.