No 1. Has to be Changi Singapore, the facilities are great (butterfly garden, swimming pool, ect)
No 2. Has to be Schipol for it’s simplicity
While Terminal-wise, the best will be LHR T5 and Changi 3 both are on par for me.
Gold: from my personal experience, the worst Airport I had experienced would be Jakarta, Bali and all other Indonesian airports to be honest. Although CGK T3 is quiet nice, other domestic terminals (except T3 and Garuda’s T2F) are like fish market!