There are several major differences between the two speeches. Brutus is a conspirator, and he has been involved in the death of Caesar. His main purpose when addressing the crowd is to convince them of the fact that Caesar's death was fair and beneficial to Rome, and that no punishment or hate should fall on the conspirators.His speech has some rhetorical devices, but it mostly focuses on painting an image of Caesar as a bad influence on Rome.
Antony has a more difficult task ahead of him. He did not participate in the murder, but he is getting a second chance thanks to the conspirators. This means that he has to show he does not disagree with their acts. However, he does not want to talk badly about Caesar. The result is a speech full of rhetorical devices that is intended to rise the crowd into opposition to the conspirators, while never openly saying he disagrees with them.