I have memberships in all of the major car rental companies.
I would value these free miles more, if rental companies would stop charging fees for when you use airline miles.I resent being charge fees to get "free" stuff.
I have an Emerald Executive level membership in National Car Rental and a great rate thru my employer. (Financial arm of a major US auto company)
I take the credit for free rentals instead of paying airline mileage fees. I generally like the options offered. New Year's weekend, I was able to select a Jeep, with real 4 wheel drive, (Manually selectable when I wanted it), for the midsize price on a rental from St Louis, because of the weather expected for the Peoria IL area, which was the destination after seeing Cats at the FOX in StL.

It is interesting, years ago, it was fairly easy to find leisure rates, thru AA or other places, with lower costs than my corporate rates
But, back then a lot of corporate rates had mileage charges. Now, my corporate rates have unlimited miles, have no drop fees, include CDW, and are usually lower than the best leisure rates.