Carving the path of least resistanceCars that are slippery through the air use less energy, especially at high speeds (air resistance increases exponentially with speed). That simple truth means that a vehicle's coefficient of drag matters tremendously. In a gas or diesel vehicle, it has a big impact on how much fuel you burn, but it matters too in an electric vehicle because it means you can drive further on the same battery size.
Case in point, the magazine Car and Driver has a feature article on this very topic. They took 5 very slippery vehicles and brought them to a wind tunnel to see which one was the true kind of air drag.
Here are the results:
Note that the Model S won over the Prius because while they had the same drag area, the Tesla had a lower coefficient of drag and a larger frontal area, so it did better starting from a disadvantaged position (smaller frontal areas offer less resistance to incoming air, all else being equal).
Bottom line: The Tesla is incredibly slippery through the air, but the Prius and Volt are also top contenders. The Nissan LEAF does well compared to many mainstream vehicles, but its being left a bit behind here. As for the Mercedes, it does very well for what it is (26/38 MPG), but it isn't nearly as green as the EVs and hybrids...