I'm choosing column 4 for several reasons. First, it blocks the potential diagonal threat from columns 1-4 where X could eventually create a diagonal connect four. Additionally, playing in column 4 starts building my own potential diagonal connect four opportunity. Looking at the current state, I notice my opponent already has a vertical connect four in column 3, but assuming we're continuing play, column 4 gives me the best defensive and offensive options. It prevents X from playing there and potentially setting up multiple threats, while giving me future connecting possibilities with my pieces in columns 1 and 2.