The OP is considering the 3.0tdi Quattro, unless I'm mistaken, I don't think you can get a Skoda or VW estate with that engine? So whilst I agree the Skoda is a great car it's not really what the OP is after.
There is much commonality between the various brands with platform sharing and some running gear etc, but the cars are different and appeal to different markets. So when the OP asked about the A6 he or she probably doesn't want a Skoda promo.
Like most VAG cars the A6 is a great bit of kit, as someone else has advised make sure if buying new you get your tow bar factory fitted if possible.
If buying used seek out a model with, leather, Navigation and Bluetooth, been standard since around 2009 - will be difficult to move on without it. Standard on new ones. There should be plenty to choose from.
I've not towed with an A6 personally but I know someone who tows a boat with his 3.0tdi quattro and he really rates it, says it's very stable.
The Audi is sounding good,sorry not interested in the skoda it just isn't my thing,just need to convince OH she wants another 4x4, she understands about the weight thing but doesn't want a estate because they remind her of a hearse!!! But I don't think a saloon will do the weight and there's the dog to think of!!
Forgot to say am looking at the second hand market,unless the OH is the one with that missing lotto ticket!!! Around 09/10 year seam to be the right money at that age and there's some that don't have space ship mileage