The biggest variable, that I have found, in dishwasher performance is soft water. The biggest culprit in the "hardness" is calcium carbonate. With a properly sized water softener, hardness is reduced to near zero grains.
I've noticed even mediocre dishwashers will generally perform well with an enzyme detergent, and water is of the right temp and soft. Calcium carbonate hinders detergents ability to hold food particles in suspension, and may leave calcite deposits on the dishes and machine.
I am to dishwashers, what Rob (Unimatic1140) is to washing machines. My hobby (unfortunately to my pocketbook) is to buy dishwashers and performance test them. Both new, sometimes, and used ones from thrift stores, people's curbside trash, etc.
Unfortunately, I don't have space, like Rob, does to ever keep more than two or three in stock at any one time and have a little mini-museum.
Since I live by myself (if you don't count three cats)I only run the machine once to twice a week. By the end of the week the dishes are pretty sad with dried oatmeal, dried cat food, residual gravy. cole slaw, etc. So I give the machines a pretty good shake-down.
My favorite machines thus far:
Late 1980's Maytag with the reverse rack loading (plates on top rack, glasses on lower), and a hard food waste disposer. Great scrub-ability and the hard food waste disposer gobbles up cat food, thin noodles, etc. Except for bones, you really don't need to scrape...just tilt off big items and load.
Whirpools and Kenmore also do a nice job of gobbling up garbage.
As far as shine factor, I have a 1999 Frigidaire, that on the Pots&Pans cycle, has four final rinses. I've had so many dishwashers that I am jaded and it's hard to impress me. But nothing has ever made dishes literally shine and sparkle like the Frigidaire. Older dishes even look new when they come out. But the down side...scrubability is somewhat less than Whirlpool and Maytag. Burned on foods don't come off as well. Large fried egg whites and big noodles can't make it through the small grid openings and sometimes a few remnants are left in the grate.
The winner for overall "maybe not great at any one thing, but overall good at everything" award goes to older GE's (models with the center tower, self-cleaning filter in the back bottom of the tub, and soft food waste disposer.)
The old GSD1200 with the multi-orbit wash arm was a fun machine. It had three rinses and even did even slightly better than the classic GSD2800 electronic, which had only two final rinses, as far as the shine factor. (I believe GE added a third rinse in 1993 when they went from the GSD 2800G to the GSD2800L model with the new control panel.)
BTW...Those of you with the tower GE/Hotpoints. Don't you find the sound of the machine soothing?
Noisy dishwashers get on my nerves. Something about the tower GE's. they are not overly quiet, but the continuous wishwashing sound is somehow comforting and familiar. Good to turn on right before you go to bed, it kinda of lulls you to sleep.
