I drove there and back a few years ago, I just went the quickest way (it had no tolls anyway). We hit Calais, headed straight to Belgium, along the E40 straight around Brussels and into Germany.
Basically the most direct motorway route and the way Google Maps suggests.
Traffic around Brussels wasn't amazing but apart from that it was a very easy drive and we were able to easily average over 100mph in Germany.
IIRC from leaving my house in Surrey to arriving just outside Munich (including the Ferry) was around 13hrs.
We left the UK at about 4am on a Friday and left Munich at about 8am on the Sunday, we had no real traffic issues to speak of despite us driving there specifically for a major sporting event.