Wow, thanks for all the info guys !!

Looks like Hertz is definitely the No.1 choice on FT.

The only thing I am still slightly confused about is whether the upgrade chances are better at downtown locations or at the airport ?

I always thought upgardes at the airport would be quite rare (as a no status/5* renter) due to all the road warrior PC members snagging the automatic upgrades ? However, Hertz obviously has more cars to work with at an airport location, so that may be an advantage.

Also, would it be safe to assume that most premium/luxury cars are rented during the week, so one has a better chance at moving up a class on a weekend rental ? Just guessing here..

Thanks
J