Audi A6 C7 - choosing the right engine
 

I'm a little confused in choosing the right engine. The priority is fuel efficiency so the engine is going to be a diesel.

My choices are :

1) 2.0 tdi 177 hp
2) 3.0 tdi 204 hp
3) 3.0 tdi 245 hp

I don't know the exact figures of fuel consumption (if someone could point them out that would be great) but I heard that the 204 hp engine is more efficient than the 2L model (which is kinda hard to believe).

Does the 204 hp model come with quattro ? (im not really a fan of FWD)

you are probably splitting hairs worrying about which will give you better mileage, it is the same car and pushing it down the road is going to take the same amount of energy, how you drive may be the bigger factor in the overall mileage you achieve.
That said, if you live in a city and the majority of your driving is stop and go with long idle times at stoplights....you may use less fuel in the smaller displacement engine, because when you are not moving or moving real slow is when the smaller engine will save you some fuel, but if you do mostly high way or even an even mix I would opt for the larger engine choice, they may gear the smaller engine different which may make the larger engine give better mileage at higher speeds. I had a diesel truck that would give better mileage at sustained 75-80mph highway speeds than it would at 55-65 due to poor torque converter lock up at the lower speed and maybe less turbo boost at the lower speed....