Well, certainly you'll want a model that's compatible with whatever's driving it. Many recievers don't like low impedance loads, so generally you'll want to stick with 6-8 ohm speakers. My advice would be to stick with the same brand; it's very important that the front three speakers be well voice matched. Although even different model lines by the same company sometimes sound different enough as to compromise the presentation. For example, my Monitor Audio Silver Center didn't match my Monitor Audio Gold Ref 20's closely enough to work with music, although it wasn't terrible with movies (not perfect, though).