Up until this weekend, I would have voted for the intersection of A81 and A8 near Stuttgart, or A5-A8 near Karlsruhe. But now, my vote easily goes to the interchange of A24 and A10 northwest of Berlin. There's a massive amount of construction right now that slows traffic down to a crawl. Even worse, if you're driving from the west and you need to turn onto A10 in the direction of Magdeburg and Leipzig, the off-ramp is currently blocked off. You have to get off on the next exit and take some very narrow backroads through the Brandenburg countryside. It adds a solid two hours to your driving time. This is not a route many people on this website are likely to take, but if you find yourself driving around Berlin this summer, try to avoid it.