Blue is prettier, stainless is easier to clean. That about sums it up for me. That's not to say that I don't like 'em both (I don't have any nickel guns at the moment but that's only because the opportunity hasn't presented itself), I do.
I own a few blues and a few stainless. I shoot all of them and I'm a fanatic about cleaning each of my guns after a trip to the range. I'm not happy if it isn't spotless. I find my stainless guns to be much easier to clean. It's just easier to remove dirt when one isn't worried about removing the finish along with the dirt. And, although I'm VERY careful about cleaning my blued guns' finishes, I notice that all of them show gradual erosion of the finish with time, particularly at the ends of their barrels and along the front edges of their cylinders.
Recently I bought my first 1911, a blued S & W model. Love the gun, but, as with my revolvers, I'm beginning to see the first telltale signs of wear in the finish.