Kenan or QC?

QC pretty much depends on the terminal. There are some corporate owned terminals that will have about the same pay bennies, etc. But most of their terminals are called "Affiliate Terminals". Pay, bennies etc. can vary widely between these terminals. Equipment maintenance can differ too. I would talk to the terminal manager where you would sign on and find out what and where you'll be running, pay etc. Qc is not a bad company. I worked for an Affiliate Terminal for a few years and had no complaints.
As far a Kenan, many consider them the scourge of the tanker industry. But they do seem to have good equipment and have the resources to keep you running.