Typical mid-size vehicles might include a Pontiac Grand Am or a Nissan Altima. A full-size rental might include a Ford Taurus or a Chevy Impala. A mid-size vehicle with one rental car company may give you more room than a vehicle in the same class with a different company.

Current models in this class include the Chevrolet Silverado 1500, Ram 1500, Ford F-150, GMC Sierra 1500, Nissan Titan, and Toyota Tundra. Those form the backbone of the pickup truck market.

According to the U.S. Department of Energy, diesel engines offer 30- to 35-percent greater fuel economy than comparable gasoline engines. Diesel fuel also has higher energy density than gasoline, which means less fuel is required to generate the same power as gas, improving overall fuel economy.