This list is 11 months old but not much has changed since.
WORLD’s WORST TERMINALS:
1. New York JFK Airport Terminal 3
2. Manila, Philippines Airport Terminal 1
3. Moscow Sheremetyevo Airport Terminal B/C
4. Nairobi, Kenya Jomo Kenyatta International Airport
5. Paris’ Charles de Gaulle Airport, Terminal 3
6. Amman, Jordan Queen Alia Airport
7.New York LaGuardia Airport Terminal 5
8.Terminal B at Newark Liberty International Airport
9. Paris’ Beauvais Airport
10. Chicago Midway Airport
WORLD’s BEST TERMINALS:
1. Jeddah (Saudi Arabia) Hajj Terminal
2. Leifur Eriksson Air Terminal, Keflavik, Iceland
3. Seoul (South Korea) Incheon Airport
4. Wellington (New Zealand) Rock Terminal
5. New York JFK Airport Terminal 5
6. Singapore Changi International Airport Terminal 3
7. Marrakech (Morocco) Menara Airport Terminal 1
8. Madrid (Spain) Barajas Terminal 4
9. Carrasco International Airport, Montevideo, Uruguay
10. Bilbao (Spain) Airport Main Terminal
CLICK ABOVE LINK FOR THE EXPLANATION
It should also be noted that one of the things which makes Singapore Changi International such a great airport is superb security organization. You don't even know you are being watched and profiled. Each gate has its own security clearance as people assemble to board. You will occasionally get wanded a second time, but generally by a beautiful shapely Asian girl who is about as pleasant as your typical unionized TSA slob is unpleasant.
The worst I’ve ever been to was Atlanta. Awful wait time and uglier than hell. Of course this was 5 years ago, they could have spiced it up since then.