The phrase "most syntactical" refers to something that is heavily focused on structure and grammar. Some synonyms for this phrase include "most grammatical", "most structural", "most linguistic" and "most syntax-oriented". These words all convey a similar idea, emphasizing the importance of syntax and structure in language. Other related words include "most systematic", "most methodical", and "most ordered". These all speak to the idea of precision and organization. Ultimately, the use of any of these synonyms depends on the context in which they are used and the particular nuance that the speaker or writer wishes to convey.