Versus is a Latin word that means "against" or "in opposition to". It is used in English as a preposition to indicate that two things are being compared or contrasted.
For example, you could say "The Yankees played the Red Sox in a game of baseball" or "The Yankees versus the Red Sox was a great game". In both of these sentences, versus is being used to indicate that the Yankees and the Red Sox are being compared or contrasted.
Vs is a shortened form of versus. It is often used in informal writing, but it is not as formal as versus.
Therefore, you should write versus in a paper.