Based on just my experiences over the last year:
Worst – UK: Nottingham East Midlands – huge queues, full of peasants, hopelessly inadequate facilities, hugely expensive car parking
Best – UK: Birmingham – pleasant and quick experience, especially in the Eurohub (but why oh why did Duo have to collapse? What a shame!)
Worst – other: Algiers – hot (no air con), endless mindless security, queues, no politeness from anyone, no facilities other than hard and uncomfortable chairs and a minute duty free shop. Close second worst – Dubai.
Best – other: San Francisco – excellent international terminal, 30 minutes from my international flight blocking on until I was in a hotel, including going through US immigration, baggage claim and customs and getting the shuttle bus. Pleasant departure facilities including no queues for checkin, nice lounge with views over ramp. Close second best – Athens.
Andy