Filters
If you get a machine without filters (Roto-Racks/DM machines, GE Potscrubbers etc), make sure it is one with a rinse-aid dispenser, that is adjustable, or dispenses plenty of agent to ensure the stuff it slipped away. I found that worked great when I needed the replacement filter on our machine, although coffee grinds are a little stubborn still ;-)
In regards to GE machines, member "bwoods" seems to have fixed that issue on his GE-2800, where he installed a dual pump setup to completely drain the water out of the sump, eliminating that .5 gallon carry-over between fills.
In the archives, another member posted the results of baked on food stuffs in these supposedly "hopeless" DM machines - the results were great, even if I do say so myself, as were results from the "Machines of Ill Repute" series - where the Wards machine left most dishes quite clean (IIRC).