Why, in Julius Caesar, was Antony’s speech more effective than that of Brutus?
Antony's speech appealed to the crowd's emotions, while Brutus's was clinically logical and direct. Brutus used language that was clinically sensible and provided a rational explanation why Caesar had to be assassinated. He told them that he and the other conspirators had acted for the good of Rome and prevented them to be ruled by a possible tyrant.
In contrast, Antony used all the persuasive techniques to sway the crowd. He used repetition, for example. In saying "Friends, Romans, countrymen," (the power of three) he is essentially repeating the same word but its effect is to emphasize the fact that he is one of them and shares their sentiments. By doing this, he draws the crowd to him -- they have the same identity and are, therefore, essentially the same.
Antony subtly uses irony. He repeatedly refers to Brutus and the other conspirators as "honourable men." The repeated use of the phrase immediately contrasts with deeds which are far from "honourable," and the crowd soon responds to Antony's suggestion that the conspirators are, indeed, not "honourable." Antony mocks Brutus and the conspirators throughout his speech by using innuendo. He never directly says anything bad about them.
In addition, by using contrasts, Antony is making the crowd increasingly aware of the brutality of the conspirators' deed. This makes the crowd restless. When Antony uses rhetorical questions, he makes the crowd think about what Brutus said and compares Caesar's deeds to that. It gradually dawns on them that Brutus had been misguided and was wrong in his judgment of Caesar.
The cherry on top is when Antony provides proof of Caesar's generosity by reading from the general's last will and testament. He informs them that Caesar had generously provided for them all in his will. This presents the crowd with evidence that Caesar was not the ruthless and selfish dictator that Brutus claimed him to be. Antony created an awareness in the crowd that Caesar truly had them in his thoughts. Caesar celebrated his victories by extending gifts to the general populace.
In the end, the crowd has been driven to a frenzy and turns into a ruthless mob that demands justice for Caesar's murder.
Part of the reason why Antony's speech was more effective than Brutus's speech can be seen from a historical perspective. Here is a little background.
Caesar was considered a populares. This was one of the two political factions in Rome during this time. The other was called the optimates. The populares favored the poorer people and their base of support came from the lower classes, which was the majority of the population of Rome. So, when Antony is speaking to the people, he is actually speaking to people who love Caesar to some extent. They have seen his benefits.
Also the speech itself underlines two important qualities of Caesar, namely his love for the poor and his generosity. Moreover, it shows of the greatest qualities of Caesar - his mercy or in Latin (clementia).