Best was probably Vienna International Airport. It's just very clean and modern and has excellent transport links.
Worst is Gatwick. It's dirty, old, not very nice to work at either and the security officers are all jobsworths.
Vienna? Really? I didn't think that much of it. We had a house in Vienna and used to fly there at least once a month. It runs smoothly until delays or cancelled planes comes into play .. an hour later and it's at the point of melting down. I did enjoy the adult shop there though

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Anyway, my favourites then.
Bratislava Stefanik Airport - They just opened the new terminal last year and it's minimal, spacious, clean and quick. Which is basically all I want from an airport.
Bergen Flesland Airport - Used to fly into it, well, at one point, once a week. Immigration is super super fast. You have your luggage ready and waiting once you're through and out of the airport in no time.
Amsterdam Schiphol - Huge, easily laid out with excellent customer service.
Worst:
Cape Town International - It wouldn't have been so bad had the immigration hall not been such a mess with moronic security guards poking around in the queues asking if you had a valid visa, as if you'd be let on the plane in the first place without one, if you needed on that is. Or asking my SA passport holder mate if he had a return ticket. To where mate? Transport links don't exist at all and every shop tries ripping you off. Price tags appears to be ballpark suggestions.
Doha, Qatar - Hot as hell with crap air con. Even at 4am in the morning I was sweating my cob off. Idiot security guards that keeps harassing with stupid questions.
Malta - Filthy. Full of flies. Taxi drivers harassing you from the moment you step outside.
Athens - Same as Malta. Better transport links to city centre via trains though.
Rome - Chaos.