What's the most efficient car?

Who said we hate foreign cars?  I have a Hyundai Elantra and my previous car was a Nissan Sentra. 

A lot people dislike foreign cars, because they tend to be small. And parts for repair are expensive. And some people just believe you should buy American cars.
I would say the most efficient car is a plug in car....

I'll go with Fred Flintstones car. 

Efficiency is a slippery term. If you mean the cars which have the greatest fuel efficiency, here is the list

https://www.fueleconomy.gov/feg/best-worst.shtml

However, there are other ways to measure efficiency. For example, mass transit such as busses, trains and aircraft burn far more fuel per unit distance than a car. But they also carry far more passengers/cargo. If one normalizes for capacity, most commercial aircraft have fuel economy equivalent to about 80mpg-100mpg (about twice as efficient as a Toyota Prius).

https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#Example_Values

US people do not hate foreign cars. Foreign nameplate automobiles make up over 50% of the US market (and significantly higher in some regions). There is a small vocal minority of domestic car partisans who make US "hatred" of foreign cars seem greater than it is. Also, the definition of "foreign" and "domestic" is extremely blurry nowadays. "Japanese" car maker Honda makes much of its US product line (and the engines for the cars) in Oho, while some Ford/GM/Chrysler cars are assembled in Canada or Mexico with engines shipped from China or England. So which car is more "foreign?"