The term "most second-string" means someone or something that is not the primary option or the highest quality. Antonyms, or opposite words, for this phrase could include "top-notch," "best choice," "number one," "first-rate," or "superior." These terms reflect qualities such as excellence, quality, and superiority. Other antonyms for "most second-string" may include "cream of the crop," "best of the best," "elite," or "creme de la creme," which signify the highest levels of achievement, talent, or quality. In short, the antonyms for "most second-string" express the opposite of mediocrity and highlight the best that someone or something can be.