BMW > Mercedes > Audi, in the game and real life.
BMW's are the best to drive overall... I don't think they make a bad car to drive (though some like the X6 are a bit suspect styling and purpose wise). Mercedes a close 2nd and in some classes better (IMO, S Class > 7 series for example).
Audi, hmmmm, great interiors and build quality, but that's all you can say positively about them with the exception of the R8 and last generation RS4.
Other than those 2, they just aren't in the same league to drive when compared to BMW and Mercedes... rubbish steering, over servoed brakes, no suspension compliance and permanent understeer whatever you do to try and avoid it. Plus they all look like slightly bigger or smaller versions of exactly the same car.