The best mpg car I ever had was a Honda CRX-HF. Miserly little two seater with a 1.5L engine and a 5 speed stick got 55 highway and 40 in town. Used to have shut off the a/c when passing on a hill. At 70 mph, it was turning 1400 rpm's and using only 13 of it's 65 hp.

The best American mpg car was my 91 Taurus, 3.0 L six auto. On a trip to NY via I 81 I got 31 mpg while using cruise control set at 70 mph. It was a good car that unfortunately died at the hooves of a big ass bambi.