The phrase "most quick thinking" implies a person who is able to make fast and rational decisions under pressure. Synonyms for this phrase may include "most astute," "most sharp-witted," "most resourceful," "most nimble-minded," "most adaptable," "most intuitive," "most savvy," "most clever," "most sharp," and "most quick-witted." Each of these words describes someone who is able to think and act on their feet in a situation where time is of the essence. If you're looking for a word to describe someone who is quick-thinking and able to handle unexpected situations, any of these synonyms would be a good choice.