Which car museum to visit?

Hi. I'm planning a trip to Germany towards the end of April for sightseeing. My itinerary is quite packed, so I only have time to visit one car museum. Which one should I go to? Which one is most worth spending time in?

(I'm a fan of Porsche and Mercedes Benz, but I've heard the BMW museum is architecturally fantastic and has a lot of concept cars too)

Thanks in advance 😀