The Buick LaCrosse is a good highway cruiser. Look for the V-6 engine, not the 4-cylinder mild hybrid. (Really - open the hood to check.)
The Dodge Charger and Chrysler 300 are from the same platform and share powertrains. The available options can change the character a bit but Avis probably won't spend much in options. A V-6 Charger has nothing on a V-6 300; take the latter every time.
The new Chevrolet Impala (again, look for the V-6 vs. a base 4) is very good, with lots of room (better packaging than LaCrosse or Ford Taurus) and a very quiet & controlled ride.
A Ford Taurus in Limited trim is competent and classically American but a little bit dated in this group.