I'm choosing paper because the opponent has shown a tendency to play rock when the stakes are high (rounds 3 and 8 were ties with rock). Given that this is a critical round 9 with the scores tied, they might go with rock as a "safe" option. Additionally, they haven't won with scissors yet, which might make them hesitant to choose it in a high-pressure situation. Paper gives me coverage against rock while accepting the risk against scissors.