I choose their best seasons as their 6th season each. Each played about 40mpg and while McGrady was more spectacular, Peja was more efficient.
McGrady scored 32ppg on 46% shooting and taking 24 shots per game. He also added 6 rebound and 5 assist.
Peja scored 24 while hitting 43% from deep and 7 less shots per game. He also added 6 rebounds per game.
If you were making a starting 5, Peja's shooting would be huge.