Is there a nice area to stay around the Athens airport or is it best to travel to downtown Athens? I'll only be staying for one night.
Do you plan to see any of Athens, or are you just on a layover/catching a flight elsewhere?
If you want to see a few things you should stay in the city. Maybe in the Plaka which is touristy but very good location - maximize your time! That way you can more easily see some sights, eat, stay out walking in the evening, and get to your hotel easily/quickly (I don’t know about later night transit to an airport hotel).
If you really don’t want to go into Athens, which is a 40 minute metro ride, it might be worth considering the Avra Hotel in Rafina. They have a regular free shuttle to and from the airport and Rafina has several nice restaurants.