Depends on the location. LAX seems to have the best mix of luxury cars on the aisle.

I most often rent from EWR and Hertz PC often has better selection. I've gotten Jags, Land Rovers, and Infiniti from Hertz this year whereas I've only seen a luxury car on National ES section once this year.

That said, your odds of getting a 7 seat suv is better at National than Hertz.