Verizon would be the top of my personal list. Any sort of billing problem and you find yourself descending into the lowest level of Dante's hell with no escape in sight. I literally spent upwards of 12 hours total trying to work through a problem with them last month. They have the art of not fixing a problem down to a science.
The problem is NOBODY does customer service any more so there aren't a whole lot of alternatives.
If you get a chance read through some of the forums linked above where customers detail complaints. It's pages of pages of similar issues followed by a comment from some "customer" of that service named "Verizonrokz" taking everybody else to task because they're too stupid to understand what a great company they're dealing with and that we're all lucky just to be able to send them our checks every month and use their services. **Cough** PLANT **Cough**