The Big German 3 are Audi, BMW and Mercedes.
Audi is known for their hallmark interiors. Audi interiors in every class ranging from the A3, A4, A6, A8, TT and Q7 set the standard. Aud's expertise in this specific category is so great that even Lamborghini (owned by Audi) has been praised with wonderful interiors for the Gallardo and Murcielago. Lamborghini features identical Audi HVAC controls and switchgear.
The Audi A8 is truly blessed with a simpy amazing interior. The A8 interior is ergonomically best in class and the MMI is the most intuitive out of Mercedes' COMAND and BMW's iDrive. Not to mention the quality of the interior and variety of textures creates a harmonious interior which can't be found in any other car this side of a Bentley.
Audi is the leader when it comes to interiors. In fact this statement is so true that I had asked for members of this forum to provide an article, review or test regarding a Model Year 2000 or later Audi which had an ergonomically poor, cheap feeling and un-intuitive interior. That article was never presented and actually does not exist. Audi won 3 awards from Ward's Auto regarding their interiors this year alone.
With cars like the RS4 and forthcoming R8, the previous belief that Audis looked great but never drove as good as they looked will be put down. The RS4 is already the best-driving Audi according to numerous magazines. The R8 if having some of the same characteristics will be an incredible sports car.
BMW has been the leader in driving dynamics. BMWs handle the best out of the luxury-sport sedans. They provide a good amount of straight-line acceleration (though not as much as some of the respective AMG models) and also offer wonderful handling and track capabilities (which most Mercedes models can't match). BMWs may have styling that isn't appealing to some, but the BMW trademark of amazing handling is always present.
Mercedes in particular with their AMG division offers cars with massive engines, huge horsepower and torque resulting in lightning quick straight-line acceleration numbers. Although quality has taken a hit as of late, Mercedes never fails to impress with their straight-line grunt.
If you put these 3 characteristics together the Germans are a true force. They have dynamic exterior designs (with BMW), clean and skin-tight exteriors with Audi and pleasant designs with Mercedes.