The old Athens airport (chaotic, dirty but also with various unused corners and benches) was great for that.
The new one is good in that they don’t make any flight announcements, but unfortunately they make security announcements every 2 seconds (same goes for any airport anywhere in the world after 9/11 I’m afraid). Also it has very few benches where you can lie sideways, most of the seats have handles.
The old Prague airport was great, you could get a shower and it was very quiet, unfortunately the seats weren’t too comfortable, but I knew of a bench behind the car rental booths and nobody bothered me.
The new one is busy and noisy and you can’t find a quiet corner anywhere.
I’ve had a good night’s sleep at Manchester airport, but that’s because I had a sleeping bag and just found a nice clean piece of floor out of the way somewhere. I don’t remember the seats.
Frankfurt it a nightmare, though I know they’ve rebuilt it since I was last there.
Leipzig is ok I guess, Dresden is generally quiet and you could probably find a corner to sleep in somewhere (though I lived in Dresden, so didn’t need to do that)
Been to many others, but can’t remember particular details, never had to spend more than a few hours in them. Trying to even remember them I realise they’re more than I thought (over 50).
Out of the more memorable ones, I’d say the old Ruzynye in Prague was the best for me, the Frankfurt one is the worst. Having said that, spending a night in Frankfurt you’d at least be able to get something decent to eat, whereas at Santiago de Compostella everything was closed.