I dont personally ride one, but a lot of people on my team ride cannondales and love them. I DO like the way the frames look. The welds are so smooth that it looks like one piece of metal. Im not saying that makes it a better frame, but it might suggest something as far as how much pride they take in building frames.
I love my Giant, havent had a problem with it since I've put about 4-5k miles on it. I used to have a Trek and wasnt a huge fan, but I think it was mostly because it was too big and had crappy components.