It is a simple question but not one that is easily answered. The trouble is separating brand identity from the aesthetic merits of the actual logo and its integration.
I have come up with the following considerations as being vital to a good logo
For that reason I nominate the Citroen logo
It has a great history; it is supposed to resemble herringbow or double helical gears after Andre Citroen acquired the patent for the invention. It has proved infinitely adaptable both to changing aesthetic fads (3d logos of the 2000s) and can be integrated in myriad ways for different cars and corporate styles.
It can cover the whole grill, such as in the Traction Avant (Light 15 or whatever taxable hp was the real name):
Modern Citroen use a different integration:
It can also just be stuck in the center of the grille like most logos:
For this reason, I crown Citroen the king of good automotive logos. What other companies deserve recognition?