Virgin Atlantic - their London base is outstanding, SAS for their extremely fresh and clean airplanes, Lufthansa on their Frankfurt-New York all business class flight, AA for their massive network and incredible all over performance - you gotta love the Dallas terminal, BA for their Concorde class - once you've flown it you know what superiority and Brittish Aristocracy is all about.
Worst, so many it's not even funny. Northwest when they still flew DC10 accross the Atlantic, Lufthansa economy class, never, never ever set foot onboard a Ryanair plane and never will - they still qualify among the worst, Southwest for their dirty shitty planes and constant ability to lose luggage even on non-stop flights, Air France for their unprofessional stewardesses and their unwillingness to speak English. Oh don't even get me started, I have so many on my no-fly-list.
