LHR Term 3 has to be up there at the top of the list. What a dump! Hardly a good advertisement for Betty's Kingdom for all those foreign wallahs.
Abu Dhabi used to be good a couple of centuries ago but has turned into a grotty backwater now.
Dubai absolutely splendid except when you are a transit SLF. Arrive at Gate 1 on the bus and told that you have 5 mins to get to Gate 35 where bus back to ac leaves. Ignore 'mover' handing out transit tags and instructions, dive into duty free, smoke cigar rapidly and then join queue at Gate 35 and stand around for 45 mins!!
Bandar Seri Begawan OKish unless you arrive at dead of night.
Perth (International side) clean, modern, good parking (but expensive), efficient and not crowded.
Downside can be the customs and immigration jobsworths
Changi (any terminal) - absolute tops
Just shows what a benevolent (apparently) dictatorship can do!