B8 Audi Avant here, so same model as the one you’re looking at (although mine is just before the model changeover to B9). Audi wins hands down, and I say that as a former late-model Mondeo owner, if you’re looking at ride, cabin quality, seats, systems integration- all better in the German.
Slightly less engaging to drive, but its an estate so. Slightly smaller interior, but neater overall, and you can see where it all went- the materials, sound proofing, fit and finish. There’s a reason both the cars you’re looking at are the same price. Bar an A/C compressor repaired under warranty, mine has been flawless to its current 110k miles, still shifts even with the CVT, returns around 45mpg overall. I won’t be changing it any time soon.
In saying that, the Mondeo is 5 years younger and is a very nice car, and is less liable to cost you money- age/condition is important- I’d probably go with that if it was me.