The first and most important thing to consider in a dishwasher is the type of dishwasher. There are basically three different types of dishwashers, portable, semi-integrated and integrated. Portable dishwashers, are just that, portable. They can be easily carried and moved about, and are ideal for singles and couples or very small families. They are also called freestanding.
Integrated dishwashers are for people who like to have their kitchen appliances blend into the surroundings, and they usually have a panel that covers the front or door of the dishwasher. Integrated dishwashers usually have their controls located inside the dishwasher, in contrast to portables, which have their controls outside.
Another important point to consider is the size of the dishwasher. If you live alone or with one or two others, a small dishwasher should be your focus. This is because dishwashers should be run at least once a week, to keep them lubricated. With a big dishwasher, dishes and cutleries may be left to accumulate for over a week before the dishwasher is run.
Other features to watch out for include the noise rating, timer functionality, and energy rating. The noise rating is good to reduce the disturbance from the machine while functioning, especially if you run the machine at night to save on power. The timer functionality is useful also to set the machine to start working in the dead of the night. Most kitchen appliances come with energy ratings now, and the dishwasher is no exception.
The more efficient the dishwasher, the less electricity used, and thus, the more savings from utility bills. Cheaper washers may have worse energy performance than expensive ones, and you could end up losing in the long run.
Finally, the machine is meant to wash your dishes, so, it's actual dish washing performance should be the most important feature. Does it clean dishes well and effectively, does it disinfect dishes and cutlery, does it perform hard food disposal? Some dishwashers scrape stubborn stains off dishes before washing. What water temperature does it perform best at? Most dishwashers wash best by using water heated to between 55-65 degrees Celsius or 130-150 degrees Fahrenheit.
A point to remember when you've finally purchased your dishwasher, is that not all utensils, dishes and glassware are dishwasher safe. You might have to discard all crockery that is not certified dishwasher safe to prevent accidents.