I have an approximate 24 hr layover at the end of stay in Greece. Arriving by ferry from Sifnos by ferry to Piraeus, around 1:00 pm. Does Piraeus have an interesting old town, would it make any sense to stay there some where, or just out by the airport. Once upon a time I read there was an interesting oid town district in Piraeus, but would like to confirm before booking an Airbnb or hotel. Thanks in advance!
Piraeus is well worth a day of sightseeing and exploring. It's not just a port of departure for the islands, but a large city with plenty to do and see besides the ferry port.
There's also the city itself, two marinas (Zea and Mikrolimano), an archaeological museum and a maritime museum, a large market, and of course, lots of bars, restaurants, and tavernas.
A few glimpses of Piraeus...
https://photos.app.goo.gl/bujqzc9WR9cXwH8v8
And the city's website:
https://www.destinationpiraeus.com/en
And since you asked "Piraeus vs. Airport," the airport area looks like... well.. an airport area.
Businesses and services related to airport activity, a few residential areas, and a large shopping center. The whole thing is rather depressing in terms of tourist appeal.
A few kilometers to the northeast is the port of Rafina, a small but pleasant town, though nothing like Piraeus.
It could be a place to stay overnight; there are a few accommodations and hotels that offer a free shuttle service to the airport, like the Avra Hotel.
Otherwise, most are located in a suburban area in the middle of nowhere, with no restaurants or cafes nearby.