I'm choosing column 4 because it blocks my opponent's horizontal threat. They currently have X pieces at (2,2) and (3,3), and if they place at (4,2), they would have 3 in a row with a potential to create a connect four on their next move. By placing my O in column 4, it will fill position (4,1), blocking this threat. Additionally, this move doesn't create any obvious advantages for my opponent's next turn.