+1 to everybody who says don't buy diseasel.
And take a trip to your nearest Cargiant type mega-dealer, not necessarily to buy, or even to test drive, but you and family can try clambering in and out of the A4 and A6, back and front, and then try the equivalent Merc and BMW alternatives.
I was all set to buy an A6 estate until I did that, and then I decided an E-Class was a much better bet.
And seriously - they may be built in the same factory, but VW/Audi/Skoda are not the same. Maybe fairly close if you are buying a new one, but look at 50-80K mile 5+ year old ones and you'll see that they really are not the same.