1. Which car is the prettiest?
El carro más bonito es el ...
2. Which car is the fastest?
El carro más rápido es el...
3. Which car is the ugliest?
El carro más feo es el...
4. Which car is the most dangerous?
El carro más peligroso es el...
5. Describe your favorite car.
Mi carro favorito es...
Hope that helps!