We bought a Kitchenaid mid-range model (s/s tub was a must) and it has worked quite well. There are two of us with no kids, so we actually bought a second set of dishes so we can run it with a full load. I think we've had it for 3-4 years now. It is quiet, but I wouldn't call it whisper quiet. Nothing that is intolerable noise-wise though. We live in a small place, and the dishwasher is literally beside our living room, so we often just put it on the 4 hour delay and it runs during the night.
Dishes come out nice and clean, and every now and then we run a dishwasher cleaner through it to clean out any gunk.
Along the inside of the door, a bit of sludge can accumulate over time, but nothing a good wipe doesn't cure.
Bosch are supposed to be very good machines, quiet, but also a bit pricey. The odd thing is that the tub capacity seemed kind of small compared to ours. Perhaps that is a function of the insulation they build into it.
We did look at the Kenmore Elite units, and heard good things about them too. If I understand correctly, Whirlpool makes them for Sears and are the equivalent to the Whirlpool Gold series (their top of the line, but at a discount from their branded models).
One question I'd like to put to the group is what detergent do you use?
We tried to go the "natural" route, and tried a few different powder and liquid varieties from the natural food stores (Whole Foods, etc), but to be honest, they just didn't do a good job of cleaning. Actually, its kind of a funny story. We started using the natural stuff right away, and thought we had bought a crappy dishwasher because the dishes weren't clean. After switching to the conventional stuff, we realized it was actually the detergent and not the unit itself.
We used liquid Cascade for awhile, but we have switched to the Finish "all in one" pucks and they do a great job. And these are the "regular" pucks, and not the Quantum ones you see the commercials for. Those are considerable premium over the regular, but regular ones work quite well. Costco has tubs of them for a VERY reasonable price, much cheaper than anywhere else, even Superstore if memory serves. They work out to something like $0.20 apiece.