I have a choice between using Avis and Hertz for my car rentals. The cost is comparable, so I'm wondering which one I should use from a points/loyalty perspective. I have memberships in Avis Preferred and Hertz Gold Plus, but haven't accumulated anything significant in either one.

Two questions:
- What are the benefits of each program, and which one is most rewarding?
- It sounds like I have to choose between getting airline miles or credit in the rental car company's loyalty program? Which is better? Normally I'd prefer the airline miles but only if they're of equivalent value.