I now use Rogers, even if they are more expensive, because I always get someone in their Toronto office and easily can speak to someone with authority to make decisions in the Toronto office.
I have had extremely shitty customer service from both Bell and from Rogers. They both lie. They both tell you they're doing something, and do nothing. Neither one of them really cares whether your connection works, and the goal of their customer service reps is the same--get you off the phone as fast as possible, preferably after having sold you an extra service.
I have had bad customer service from the 3rd party resellers as well--their favoured tactic is to blame everything on Rogers or Bell. Half the time it's true, but that's what they say 100% of the time.
At the end of the day whether or not you have a good experience is going to depend on one thing only: What's the quality of your connection?
If you have a shitty connection to their CO then you will always be calling them, and complaining about their shitty customer service--whichever company you go with--because you will always have reasons to call them, like constant disconnects, or shitty bandwidth. If you have a good connection that just works, then the few times you need to call customer service to deal with easy things like changing the credit card they bill, or upgrading your service level--well that's going to be fine.
I can't stress how important it is to find out the quality of the line between you and the CO, and go with the best quality line. At the end of the day that's the only thing that really determines your service quality. Unfortunately neither of them will EVER tell you about the quality of their line to your house--the only way to find out is to get the service and measure it, or check around and see what your neighbours have, and whether they are happy. Which one is better is different on different streets, sometimes on different sides of the same street. Depends how far that piece of copper has to run to get back to their CO.
If one of them has a CO that is 100 meters of copper cable from your door, and the other one's CO is 800 meters of cable away--they will both sell you the service, and at the same price, but one will be 100 times better than the other.