The phrase "most penny-ante" implies something small and insignificant. Its antonyms, therefore, would denote importance, significance or grandeur. Some possible antonyms for "most penny-ante" include "grandiose," "majestic," "extraordinary," "remarkable," "gigantic," "powerful," "impressive," "monumental," "substantial" and "tremendous." These are all words that describe things that are substantial, significant, or large, and that have the potential to make a real impact or impression. While "most penny-ante" might evoke a sense of dismissiveness, these antonyms suggest weightiness and importance.