With Hertz, you can reserve a midsize car (or higher) and pick from any vehicle in the President's Circle section. For that reason alone, Hertz is probably better in our opinion. Some folks will tell you that Hertz's customer service is terrible (and they wouldn't be wrong), but tbh, if you skip the counter as a PC member and choose your own vehicle, you won't really interact with them, so as long as something doesn't go wrong along the way, you're still probably better off with them over Avis.