I do not have any Kitchenaid appliances to compare it to but I can tell you that I have 2 Bosch 500 series wall ovens and I have had nothing but issues with the quality of the stainless since I got them. I just had a repairman out to my home for the 4th time with replacement doors and he even refused to install them when he saw the quality of the workmanship. I cannot recommend these appliances. The stainless is flimsy in my opinion.

We just purchased all new appliances for our new kitchen and I was considering the black stainless. However, the sales guy advised me against it for all the reasons listed above. He explained how the "finish" is really just a film over stainless steel and showed an example of how it scratches on a floor model. It was enough to steer me away and go for the more traditional stainless. I have had the fridge for about 6 months and it cleans up really well with little to no fingerprint marks. The microwave, dishwasher and stove are being delivered on Saturday. All of my appliances for the past 9 years have been Whirlpool and I have been pretty happy with them.

Most appliances manufacturers seem to use some sort of brushed finish. And in practice, the differences between manufacturers tend to be not overly glaring. Sinks are a bit more of a wildcard. There are a couple of different finishes that you can get. But then, a sink is in a very different place, and accumulates scratches with use anyway. I personally don't feel it has to 100% match the look of the stainless appliances. If you are really anal, you could always have your contractor redo all the grain with a sander and some 3M pads. It's labor intensive though and does take some amount of practice to get a uniform finish. Most people wouldn't really go down this route -- and if you do, make sure you get samples of their workmanship first; it's easy to make things worse instead of better.

I think you can definitely mix them. However, I wouldn't mix them on the same wall. For example, if your fridge and your range are on one wall in black stainless, you could add a regular stainless DW and microwave in the island. If you're going this route, carry the mixed metal idea through to your faucets, hardware, and lighting, too. Lots of great photos on this site with mixed metal finishes in kitchens. All that said, I wouldn't do this if you're planning to sell the house in a few years. If it's a look you love and you will be in your home for many years to come, go for it.