Which used car with 100,000 km should I choose between a petrol Audi A4 and a Toyota Auris hybrid?

I'd recommend the Toyota Auris hybrid at that mileage, because the hybrid engine is much more robust and reliable in the long run, and maintenance costs are definitely lower compared to the Audi.

The A4 petrol is nice to drive but at 100k km little problems start popping up here and there, especially if it hasn't had perfect maintenance. With the Auris you spend less on repairs and consume less fuel, which over time makes a real difference.