If you are renting at a location that doesn't have Ultimate Choice in the US, be it a Local Edition or an airport location, the only upgrade benefit as a President's Circle member is a one-class upgrade from a mid-size to a Standard (or, most likely, a Full-Size) sedan. Upgrades to SUV or paid upgrades are going to be a very much variable and unpredictable offering on a case-by-case basis.

The following thread is full of reports from PC members renting at non-Ultimate Choice locations to help give you a general idea of what to expect: Hertz Vehicle Upgrades and Experiences for Elites Master Thread and Guide