At the moment I am using osticket.
I am searching for a support ticket systems that supports:
I want that customers can rate the quality of the support, so that unsatisfied customers can be spotted and taken care of separately by another support level. And of course to contorl the quality of support staff members
If the user feels unsatisfied with the support, there should be a possibility to escalate the ticket or to "notify someone in charge".
It can be a paid solution as well.