I checked Copenhagen airport's website, http://www.cph.dk
, and the results were from IATA's annual market survey in which 60 000 passengers took part.
CPH has been rated best in Europe several times, but has previously lost to Singapore's Changi.
According to the IATA market survey, the best airports in the world are:
Copenhagen Kastrup (CPH)
Singapore Changi (SIN)
Amsterdam Schiphol (AMS)
Hong Kong Chek Lap Kok (HKG)
Oslo Gardermoen (OSL)
I'm not too sure about the "ranking order" after CPH and SIN, and this is just information from the top of my mind, and please correct me if I'm wrong.
I've been to all of these airports (except HKG) and I can endorse IATA's passengers' choice.