megamiles: ouch! you're so young. anyway, I checked with DL regarding earning SkyMiles with car rental. Effective 01 OCT (not much warning there), all car rental partners, with the exception of Dollar, will either give 50 SkyMiles per day of rental OR one mile per dollar on a corporate/government rentals or 2 miles per dollar on other rentals. Dollar will continue giving 500 miles per rental.
The same goes for CO with the exception of Dollar and Thrifty. These car companies will still give 500 miles per rental.

As for hotel partners, Thrifty is a partner of Hilton so they are your best for getting the most points. You can rent with National but again you only get 50 miles per day of car rental. However, you do get 500 HHonors points as compared to the other car rental companies which will only give you 250 HHonors points.