I am not a big fan of Audi. Mainly, their cars tend to understeer like front wheel driven cars. Actualy Audis are mostly front wheel driven but even the Quatrro tend to act like that! Therefore, I could not love Audi. But this does not change the fact that Audi is making very good cars but I cannot say they are very efficient like BMW. You can understand this by their emission levels. BMW 320d ED (163 PS) 109gr/km, Audi A4 2,0 TDie 120gr/km (136 PS).
BMW's Efficient Dynamics technology is offering very high levels of fuel efficiency. Even the Mercedes does not offer similar technology on every model. Actually, they just started now but BMW introduced this earlier. And their new advertisement is proofing this!
A kid in primary school is talking about Efficient Dynamics and his classmates are looking with empty faces, actually when they will thirty, they will still have the empty face! Proofed :) End of the advertisement, he is showing BMW's as the most efficient cars. And focus on Audi details ;)