Leaving aside the question of just what is "best," and then how you would go about measuring that quality (since this could easily result in just about anything being "best"); instead focusing on a couple key issues that came about in the aftermath of WW2 that has had major implications on the automotive industry in those Germany and Japan.
First, as future military industry was essentially a non-factor. When the countries rebuilt industrial capacities focused entirely on other areas, it's easy to see how the automotive industry would receive a greater share of possible resources (if the US had no military industry, and all of the engineers and manufactures involved in aircraft, warships, etc instead were divided among the auto industry?). This had an undeniable impact.
Second, as part of the terms of their surrender, and as a lesson from recent history at the time, the Allies were active in helping to rebuild their capacity and provide favorable trade status for their goods (the aftermath of WW1 took an opposite approach, which was a major factor in WW2 coming about in the first place). Although this didn't provide a real advantage, it did negate much of the disadvantage that came about from literal war damages these countries suffered that would have otherwise slowed their economic and industrial development.
Third, and maybe one of the biggest and most misunderstood: worker rights and unions. Both Japan and Germany received, what would be considered today, extremely liberal Constitutions in the wake of WW2. FDR had long considered such options as possible amendments in the US, but with his passing and subsequent political changes in the US, that never happened. It did however figure into what came about in Japan and Germany - both of which have the strongest auto worker unions. As a result, the strategies of each have seldom mirrored the so called "race to the bottom" that was often adopted by US and some others, as union strength generally forced companies to look at more than just simple cutting of costs (for Japan, it was most often efficiency of production to keep costs low as Germany traditionally focuses on the efficiency to reach higher quality).