Which word fits best in the sentence: We should go and eat at "Franco's" which is ____________ a great little restaurant?

The word that best fits in the sentence is "supposedly." This term is often used to indicate a belief or assumption about something that is expected to be true, but it may not be personally verified. In the context of the sentence, it implies that there is a general belief or understanding that Franco's is a great little restaurant.

Using "supposedly" suggests that there are claims or reputation supporting this idea, even if the speaker might not have firsthand experience at the restaurant. It aligns well with the conversational tone of the sentence, making it sound natural.

In contrast, the other options do not fit the context as seamlessly. "Supposed" is primarily used to indicate something that is taken for granted or expected, but it lacks the nuance of popular belief that "supposedly" provides. "Presumably" suggests that something is likely true based on existing evidence, but it feels slightly more formal and less conversational in this context. "Assumed" conveys a similar idea of taking something for granted but is not commonly used to convey general beliefs about places like restaurants.