A public presentation is a more interactive experience than writing an essay is, during a public presentation there is the potential for a counterclaim disputing your side of the argument while in an essay you could lay out all of the facts without any way to be directly confronted where you'd have to think of your response on the spot and know your facts. Writing an essay also gives you more time to think about what you'd say and how you'd say it. I hope this helps some.
