How can Brutus be proven to be a better man than Caesar??

This depends on what point of view that you are looking at these men. The word "better" has many variables. Both men have strong traits. Caesar brought military power to Rome but became obsessed with total unquestioned power near the end of his life. Brutus was a wise and loyal servant to Caesar but more so to Rome. He felt Caesar's power was becoming obsessive. Brutus might have talked to Caesar first before killing him but decided to join the conspirators anyway. Would Rome really have been better off as a republic? I think much of your answer depends on how you view the characters and the play.