There are several different synonyms for the phrase "most contrivable." Some possible options include "most imaginable," "most feasible," "most possible," "most workable," and "most likely." All of these phrases indicate that something is able to be created or achieved, and that it is the most likely or most reasonable option available. Depending on the context in which the phrase is used, any one of these synonyms could be appropriate. For example, if discussing a theoretical concept, "most imaginable" might be the best choice, while if discussing a practical solution to a problem, "most feasible" might be more applicable.