I wouldn't call either one of the great minds of the era. Not as an insult, both highly intelligent men but just think there are others who were even greater.
I would probably go for Zhou Yu as the better strategist despite not knowing how his invasion of Yi would end up but perhaps Sima Yi (no slouch as he could be a bold strategist bar facing Zhuge Liang) the better all round mind given his political and propaganda abilities. Both perhaps strengths also lay in parts of their personality, Zhou Yu made a good commander becuase of his good nature, Sima Yi was successful becuase he had a ruthlessness that Cao Shuang (who did beat him politically for some time) lacked
“You, are a rebellious son who abandoned his father. You are a cruel brigand who murdered his lord. How can Heaven and Earth put up with you for long? And unless you die soon, how can you face the sight of men?”