For people just staying for 1 night or arriving in the late afternoon, staying near Piraeus cruise port is very convenient and a good option. You’re only minutes away from the embarkation terminal, taxi to the ship is quick and cheap. However we would definitely recommend a hotel in downtown Athens. You need at least two full days, this will give you some time to explore the historical old town, or enjoy dinner from any of the rooftop restaurants with incredible Acropolis views.