The antonyms for the phrase "most set up" also known as "most established" can be varied based on the context. For instance, "unsettled", "newcomer", "emerging," "underdeveloped," and "inexperienced" can be antonyms for "most set up" when referring to business entities. In terms of individuals, "undecided", "undetermined", "forgetful," and "disorganized" can be antonyms. Moreover, when referring to places, "undeveloped," "uninhabited," and "unexplored" can also serve as antonyms. The list of antonyms for "most set up" can vary based on the context of use.