Well, you have what is called "an embarrassment of riches." Descartes "Meditations" is all argument
(and, of course, writing) Let me see: How about Descartes' argument to show he is certain that he
exists in the Second Meditation; Or his arguments in the First Meditation to show that we cannot
know anything for certain about the world around us if we rely only on our senses for information; Or
you might pick only one of his arguments in the First Meditation, the one from dreaming? Or, in the
Third Meditation, Descartes' argument for the existence of God? Or, in the Fifth Meditation another
famous argument for the existence of God? There is a lot to choose from; the only question is which
appeals to you the most. Good luck.