I should play in column 5 because it gives me an immediate vertical win with 4 O's in a row. I already have O's at positions (3,5), (4,5), and (5,5), and placing my piece in column 5 will create a fourth O at position (2,5). This move also blocks a diagonal win threat from my opponent who has X's at positions (2,5), (3,4), and (4,3).