The original and still the best, the Toyota Prius has the best fuel economy of any non-plug-in car while still remaining a surprisingly roomy and practical family vehicle. (The EPA considers it a mid-size car based on interior space.)
It's not exactly a fun ride. The steering provides some pretty mushy feedback while acceleration is only somewhat better than a bus.
But the Prius makes up for it all with, obviously, amazing gas mileage and a nerdy-cool high-tech personality, inside and out. What the Ford Mustang is to fun, the Prius is to fuel efficiency. It remains the icon of its type.