KLIA is the most beautiful architecturally but it is a hassle to get to and from the city centre. Changi is possibly the most hassle-free but suffers from a lack of character...pleasant but dull. NAIA has a lot of character with its motley inter-island aircraft, but is a hassle in various ways...
All things considered, it probably is CLK. It is beautiful, efficient, has great amenities, has room for growth, and super infrastructure to get to the city.
That being said, my favorite airport EVER has to be
Kai Tak. No airport in the world, no matter how beautiful or spacious, can compare to the Kaitak's unique setting. I miss it terribly... I miss that hairy final on Runway 13...I miss not seeing the whole aircraft from ground level and hearing my footsteps as I climb the stairway... I even miss the aroma of sewer stench mixed with avgas and diesel when riding those ramp buses.