So you have determined you need to upgrade to a dishwasher or are in need of a replacement for your old, tired looking model. First settle the question of portable or under-the-counter models.
A portable dishwasher can be moved from its hiding place to near the sink via casters. It is finished on all sides unlike the built in models and can be used as a work surface. When its dish cleaning services are needed, you wheel it over to the sink, connect to the kitchen faucet via a quickly connected adaptor, and place the drain hose is in the sink.
Pros include its sight-unseen capability, freed up cabinet space for a kitchen with no room for an under the counter model, no installation costs, and no need for a hookup if you are living in an apartment without a dishwasher. Plus you can take your portable with you when you move.
Of course, if you have the room and money to pay for installation or the talent to do it yourself, the built-in model offers convenience and more choices. Most portable washers are of the low-to-mid range quality.
Haier America HDT18PA Space Saver Compact
Frigidaire FDB126RBB 24" Built-in
Frigidaire PLD2855RFC 24" Built-In
Frigidaire Professional Series PLD4375RFC 24" Built-In