Worst: Time Warner. Too many reasons to list here.
Second worst: Best Buy (ordering online was an absolute nightmare.)
Best: DirecTV. Many reasons, the latest of which was when I had to suspend my service due to moving. Of course, there's no charge for that. Also, credited me for my Sunday Ticket and gave me another $70 on top of that. Always willing to work with their customers (at least, that's the experience I've had.)