Which engine specifically? I love the VW EA897 (3.0TDI). Smooth engine (for a diesel or normal Otto) The fuel economy can be very good. I can get 4.6l/100km out of mine. The A8 doesn't have the really good variants, they opted for the V8 tdi instead. Either way, peak torque at 1700rpm makes the car feel more effortless than a comparable Otto engine if you aren't pushing it all the time. The tfsi does have a supercharger. The more immediate power delivery is nice but will kill fuel economy.