The worst rental car I ever got was a Toyota Corolla. We drove off the lot with it, got maybe a mile down the street, then Enterprise called us back and upgraded us to a Buick LaCrosse for free (they found out we were getting married and figured we should get something better).
Besides that, since 2012 I've rented an Avenger, an Equinox, a Liberty, and an Altima. All were fine but none could touch the LaCrosse. It was like driving a cloud.
my first job out of school was for a rental car company. One of the only good parts of the job was that I got to drive almost every make and model conceivable. Sometimes for rentals, it's not about the model of car it is that determines how it drives, but it's time in service and how much past customers beat up on it. Most rentals would only last a little over a year or a certain amount of milage before it would get pulled from the fleet and sold back to the automobile manufacturer.
In my short time there, I experienced the most mechanical and maintenance problems with Dodge and Chevy. Fords were nothing short of spectacular, I was particularly fond of the fusion, edge, explorer and mustang.