Ive not been travelling that much. Yet. So for me its Yangon's crummy airport that gets the worst airport award....
Funny, my wife and I went through Yangon airport early last year and thought it was a cattle yard.
It is very very very very bad, but entertaining in some respects.
Never before have I seen young boys/men grab passenger's luggage tags and actually fling themselves through the rubber hanging mat over the moving conveyer belt to search for the person's cases.
Best would have to be Singapore and Dubai.
Best: I'd have to say Dublin is quite a nice airport to spend a bit of time in. Although, I'll no doubt be up there with the Singapore ranks after landing there in Aug. Santiago is nice too.
In terms of feeling welcome, best would be Easter Island - lots of locals with flower garlands and music.
Worst: Sorry, but I jsut hate Stansted, mainly because I've had to sleep on the floor there more than once. And it's just a big barn.
Wasn't a fan of Newark either. Just a big horrible hub.
I have not had a great many experiences yet (just started my 1st RTW 4 weeks ago) but Barajas airport in Madrid was very impressive and well run. My only minor complaint was that it was a little over thought, i mean you have to get an underground train to get your bags! Not overly keen on Heathrow...taking the security thing a bit too far (same reason i am not going to USA on this trip - cannot be fucking bothered with the hassle).
All 3 were really clean, fast check in, comfortable etc. Had no problems in any of these.
Worst Paris (CDG) and Heathrow
No organization. Massive queues. Long distances to get around.
I haven't traveled enough to say which is worst or best.
But I like Düsseldorf International Airport. (use it a couple of times a year, and except for the costs of parking it's perfect).
Worst experience so far was at Copenhagen, where they decided to close all securityscans, except for one. This caused a long queue, on which it took almost 30 minutes to get passed the security check. after that it took very long for them to tell us at which gate the airplane would be leaving from.
I am a bit suprised to read a lot of comments, that are more about airlines, than on the airport. It's true that Ryanair chooses some deserted airport in the middle of nowhere. But blame Ryanair (and yourself) for flying to those airports. (you want cheap, you get cheap).