I can't think of any instances which would make me single out one particular company as 'the worst I've ever dealt with'. But, then again, I really don't have much reason to complain and the question the OP posits if largely subjective anyway.

The bus, to me, is simply a conduit for getting from A to B within the allotted time allowed for in the timetable. It can be inconvenient when that standard isn't met - especially when my journey is contingent on connections - but sometimes this is out of the control of the operator and most (if not all) operators have fallen foul of not running to timetable on occasion. If it becomes a regular occurrence, I am lucky enough to be able to choose my car over bus (which I appreciate is not a choice available to all - but this is based upon my own experience). Because of this, I have little experience in dealing with customer services as I simply make other provision rather than spending time complaining.

Outside of timetabling issues, I really don't care if the driver is well presented or acknowledges me when I board or alight. I am indifferent towards whether a bus has WiFi as I'm fortunate enough to have a generous amount of mobile data provided my phone operator. I would of course prefer plug sockets to be operational but, overall, it is a minor issue on short journeys. Besides, if I forget to charge my phone in the house before getting on the bus, I can hardly hold the operator responsible. As long as it gets me where I want to go I am not bothered whether the bus is branded or the correct vehicle type.

Each operator has their positives and negatives.