A lot of people are not clear with the real differences between an economy and a compact vehicle. The truth of the matter is that there is not that much difference. The economy car may be able to accommodate 4- 5 people, 1 large bag and 1 small bag or carry on. Depending on the rental agency an economy car could be a Toyota Yaris, offered by ACE, Fox and Payless. A Hyundai Accent offered by Budget, Avis, Advantage, E-Z Rent-A-Car and Sixt. A Kia Rio offered by FireFly, Dollar, Thrifty, Hertz and last but not least a Chevrolet Spark available at Alamo and National.
On the other hand the compact car may have a little more storage capacity, it can carry 5 people and 2 large bags or 1 large bag and two smalls. The features of both car types are pretty much the same. A compact car could be a Nissan Versa available at Fox, Advantage, Alamo, Enterprise, National and Sixt, a Ford Focus available at E-Z Rent-A-Car, FireFly, Budget, Dollar, Thrifty, Hertz, Avis, and Ford Fiesta available at Payless. In some cases, an economy car could also be considered a compact car which is the case of ACE Rent-A-Car that offers a Hyundai Accent or similar vehicle as a compact vehicle. The price may vary slightly typically $1-$2 per day among car rental companies depending upon availability. As far as fuel efficiency, an economy car is estimated at 23 mpg in the city and 32 mpg on the highway vs fuel economy of at least 28-38 mpg for a compact. Another difference could be that economy cars could have 2-4 doors and compact cars have 4 doors.
Finally, keep in mind that regardless of the car type you decide to rent your possibilities for a free upgrade doesn’t depend on either one of them.