The first choice you'll want to consider is stainless vs standard. The former retains heat better. In fact, we don't have to use heated drying ever with our stainless.
The next choice is heating element at the bottom or separate heating chamber at the back. The latter is less noisy and you don't have to worry about things on the bottom melting. However, you lose about 1-2 inches in your racks. Note that if your dishwasher is 15 years old, any new dishwasher is going to be quieter than yesteryear. Your next choice is buttons on the front or buttons on the top. Buttons on the top is prettier but can end up tucked under your counter. However, you push your cycle buttons before you close it and only rarely do I ever change anything mid cycle. Most models instastop upon opening the door these days. Another choice is how it deals with large particles of food. You can get one that filters it (and you'll have to clean said filter every so often, or one that chops it up. Your last choice is the configuration of the racks. Some have third roll out rack for cookie sheets and larger utensils the like. Others do not. But the extra rack does use vertical space. In some you can adjust the top rack up or down on the fly. Others, you have to pull it out and put it back in (which stinks if you've loaded it and that last dish you want to put in is too tall) Still others cannot be adjusted. There are also variations in cycles. Some have separate super duper pot scrubbing jets on the back wall, others don't.
We took our larger sized dishes in and loaded the various dishwashers to try them out. We ended up with a Whirlpool manufactured Kenmore stainless, buttons on the top, filtered, element on the bottom. The two inches did matter to us and the space lost with the extra rack also mattered. We also don't use much plastic having converted over to stainless and glass. We got the super duper pot scrubber. I don't really see that it does differently than our normal pot scrubbing cycle which does fine. We have more cycles than we know what to do with. We use energy saver pot scrubber, and old fashioned 1 hour wash the most with the vast majority being energy saver. We don't leave gobs of food on the plate so the filter does fine. It's not hard to take out and clean. It's not the quietest model but our old model was at 97 on the noise meter. So the difference between our 45 and others 42 was moot for us.
