I'm choosing column 4 because it's the most defensive play. My opponent (X) has three X's in a row vertically at positions (3,3), (2,3), and (1,3). If I don't block column 4 now, they could play there next turn and create a vertical four-in-a-row. Additionally, playing in column 4 doesn't seem to set up any winning opportunities for my opponent. The other available columns (0, 1, 5, 6) don't appear to offer immediate threats or opportunities, making column 4 the most critical defensive move.