what is the best quality in a car?

Could you please be a little bit more specific about ''best quality'? Meaning a specific part, a whole section or... ?'

i mean like in racing: is it the power, engine, .....?

for circuit racing handling/grip is the most important, for drag racing its traction and power....

The most efficient combustion. Lol.

depends on what kind of racing too. you always need grip, so suspension and tires are important.