Agree Changi is top of the heap but it wasn't always that way and it has been around since '81... constantly modified and improved with steady expansion which was planned in from the outset. I well remember shortly after the opening those weekend Bus Tours for the proud citizens out from town to check out the new miracle. (And after the Zoo that was Paya Lebar, Changi most certainly was a miracle).
Surprised nobody has gone for Seoul Incheon - nothing flash but a well designed, efficient, clean and passenger friendly airport, but 5 years in it's already too small and the new terminal is needed badly.
I also think Vancouver is great airport - innovative design and decor, great facilities and super friendly staff.