Wiktionary
winningest
a. 1 (en-superlative of: winning) 2 (context US English) Most winning; most attractive. 3 (context US sports English) Having the most wins.
Usage examples of "winningest".
I just stood there, wearing my winningest grin, confident that she would talk herself into leaving the public eye.
But because we wanted to respect and humor our winningest member, we didn't push it.