The antonyms for "most second string" would be words such as "top tier," "first-string," "elite," and "premier." These words denote high quality, excellence, and superiority. When something is described as top tier or premier, it implies that it is the best of the best and not easily surpassed. On the other hand, the term "most second string" suggests mediocrity, average performance, and lack of distinction. While there is nothing inherently wrong with being second string, it is seen as a step down from the top tier. By using antonyms of "most second string," you can convey a stronger sense of excellence and distinction.