I tend to prefer black guns (and holsters) because they seem to disappear a little better. Never the less, I have the 642.
Also have a couple of 640's that are stainless. The other day while chrongraphing some loads, I was shooting toward the sun with a 640-1 and got glare from the tang just behind the sight It prevented me from seeing my sights.
I'd get the one with the best trigger.