I like that they are very open to working with their clients, even if they don't have any experience in the same area as what you're looking to accomplish.
They also deliver on time and usually within budget. While we had some issues getting things done quickly, I felt it was more because of our own lack of communication than anything else. It's not always easy to get everything moving at once, but having people who understand your vision and can pull together all elements so seamlessly, including minor details (like font selection), makes my job easier when it comes to communicating to others about the project.