Whilst I know that my flight deck pals may disagree right now, the best airline for me would be Virgin.
I stress this is a personal thing - I never thought that I'd be doing a job that is always challenging and ultimately fulfilling, with non-stop travel to (usually) great places, no two days the same, and to be part of a superb team of people, both in the air and on the ground. VS have given me this opportunity, and everything else aside, it really is the people that make it.
Please don't flame me for this - I do get to see both sides of the coin when it comes to ongoing issues, and as I say, this is just for me!
Cheers,
Bob