a. What is best to serve at our dinner party?

b. What is the best to serve at our dinner party?

c. Among the dishes on that list, which is best to serve at our dinner party?

d. Among the dishes on that list, which is the best to serve at our dinner party?

Which of the above sentences are grammatically correct?

I think (b) is incorrect since we are choosing from an unlimited list of possibilities, however if we had 'the best thing' or 'the best dish' or something like that then it would be fine.