I've driven the new Audi A4 and yes it is a nice car but so is E90 and C-class. I wouldnt go trade my E90 or C-class becuase I think Im getting a better car if I buy a A4. All three are close to each other, it comes down to personal preferences and you cant go wrong with neither of them.
But I can understand why Audi owners are changing their old A4 to the new A4. Natural step and its a more fresh design than old A4 and a larger backseat if that is important.

I drove my BMW directly after I drove the new A4 and steering, gearbox and handling is better in my car. but I didnt expect anything else either.