To be honest, I wouldn't really care who I flew for, it's far to easy to say; "I'm going to fly for _________ when I qualify". At the end of the day its whoever offers you the job lol
The only airline I would have real concerns working for, would be FlyBe. I went to their open day at Glasgow Uni and wasn't very impressed. I don't fancy getting stuck on the props, although I'm sure they would be great to fly, it's just not what I want to do.