Ryanair is a bit of a controversial airline here in Denmark (politically), and it caused quite a stir when they announced their plans to establish a base in Copenhagen Airport. The unions were not happy, and in the end, Ryanair cancelled their plans. No sleepovers for the Irish airplanes this time around.
Ryanair turned out to be quite the popular addition to CPH, though, so I guess the travellers didn’t agree with the unions. I have never flown them, but I do enjoy watching their fleet of Boeing 737 with the very nice livery.