MS Project and Primavera P6 are simply different programs. Ok, they do basically the same thing: that is they are both scheduling tools. But the way they go about is a bit different, particularly as it relates to the user experience.
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Here is a tip to assist in your answer. Get two sheets of paper, on one, write the technical benefits of MS Office and on the other, Primavera. Once done, you will have your answer.
If this is for a business, then contact a vendor for both and compare the information that they give you.