I prefer Hertz's choice program 1000x over Avis' program where the agent decides what you get, even if you do get a one or two class upgrade. With Hertz you can just see what's available and pick whatever you want; the upgrade options are also very straightforward - $x / day to go into a specialty car, which can be a great value.
With Avis and the others, the agents seem to hate walking you through the options; you could be at an airport with a full lot and they'll be like "this is the only car available."
I am more interested in the specific make and model of car than whether it's considered to be an "upgrade" based on how they define the car classes.
I usually compare prices between Avis and Hertz, and will only go with Avis if there's a significant advantage. I don't see that plan changing with this partnership; Avis' elite program has ~zero benefit in my experience.