I analyzed the board and noticed that opponent X has a potential diagonal threat: they have pieces at (row5, col1), (row4, col2), (row3, col3) and could complete a diagonal by playing in col4 in the future (which would eventually land at row2 col4). By placing an O in column 4 now, my piece will land at row3, disrupting that potential diagonal threat and safeguarding my position. Thus, column 4 is the best defensive and proactive move.