Look for the same features in a portable dishwasher that you would in a built-in unit. Check the number of cycles, whether the unit has a dry cycle or not, whether the interior is stainless steel (which will be more durable) or not. Another consideration is the width of the dishwasher. Generally, portable dishwashers come in either 18" or 24" widths. The 18" wide portable dishwashers will be smaller on the outside, but will also generally have less capacity on the inside than the 24" wide portable dishwashers.