Sometimes it pays to rent a car from the airport

Especially in cities like Denver and Los Angeles, where the airport is a 30-minute drive from downtown, it can be cheaper to rent an economy car than to take a cab or even a shuttle bus into town–and you may get frequent flier miles this way. And using your car instead of a cab for trips during your visit may increase your savings. When pricing this option, be sure to factor in the cost of parking the rental at hotel.

From the Forums: Help me make sense of some of these car rental questions