They were ranked the lowest for customer satisfaction for 2012.
However, I would say that I'd much rather fly with the United crews than the Delta crews. I have been astonished and agog at some of the horrible, rude, nasty, threatening behavior I've witnessed with Delta crews, especially flying between Chicago and NY or Detroit and NY.
The last time, I was actually surprised there wasn't a passenger uprising against one particular FA who was threatening to have a guy kicked off the plane for asking a simple question about our flight delay. She went crazy on him and only backed down when several other passengers stood up and told her that she'd have to kick us all off. I really wish my cell phone had a video function, because I would have liked to have a video of that to send to Delta. If I hadn't seen and heard it myself, I wouldn't believe it. But shat woman had serious anger management problems and should not be in the position of a FA.