Who is the best orator in Inherit the Wind and what made their words so powerful? Can we analyze this person's speech for diction, figurative...

There are some distinct choices to this answer.  The most evident would be having to choose between Matthew Brady and Henry Drummond.  The reasons they are both so powerful of oration is that both speak from a fundamentally persuasive point of view.  Brady speaks from a spiritually driven perspective rooted in the traditional interpretation of Biblical ideology.  When analyzing his syntax and content, it is Scripture based, sometimes being able to identify specific book and verse.  Brady speaks for those who have no voice, in particular the individuals who are poor or of moderate means and believe in the power of Scripture and established religion.  His tone is reflective of this, in its authoritative and driven nature, one that shows a man who believes in the authenticity of his convictions and the passion of his beliefs.  Brady speaks for a view of the world that craves for order, unity, and symmetry and there are many a passage in the text which reflect this.

Henry Drummond speaks from the intellectual frame of reference.  Whereas Brady professes and demands that he is confident of "the answer," Drummond speaks of "the question."  His point of view is the ability to think and to reason.  Brady's source of beliefs is the Bible and the supposed word of God.  Henry Drummon's source of his belief system is the human mind and its ability to address problems and predicament through rational thought.  In his tone and diction, Drummond features a questioning, almost a quizzical approach to speak.  Rarely, does Drummond reach the fevered pitches of Brady.  Whereas the latter demonstrates "sound and fury" from start to finish, Drummond's oratorical approach is percolating, almost bubbling underneath the ground, building and swelling with logic and reason, until an intellectual groundswell gives way to a powerfully compelling display of "the ability to think, just like a sponge." This is demonstrated in the cross examination of Brady, where both styles of oration are evident and in full display.

If we were examining oration in other characters, one could examine the styles of Reverend Jeremiah Brown and Bert Cates.  The former is an orator in the fundamentalist religious approach and represents this in both style and demeanor, while the latter is reflective of the intellectual.  Their contrast would be set against one another because, unlike Brady and Drummond, there is little that one appreciates in the other.  Finally, a comparison of oration in terms of analyzing the conflict between modern and traditional conceptions of womanhood can be seen in the characters of Rachel Brown and Sarah Brady, characters whose words reflect their fundamentally changing beliefs of the demands women place on both themselves, their significant others, and their societies.