How can I understand "mit am besten"?

Question

Or more generally: mit + superlative.

Answer 1

If you only use the superlative, e.g. in "Dieses Auto ist am besten.", then you're referring to one person or thing that is THE best ("This car is the best."). But when you add in "mit", e.g. in "Dieses Auto is mit am besten.", you're saying that the car is one of the best, i.e. there are others that are also very good.