I'm choosing column 4 because it serves two purposes: 1) It starts building a horizontal sequence with my existing O pieces in columns 1, 2, and 3, potentially setting up a win. 2) It blocks a potential diagonal threat where my opponent could play in column 4 and then follow with column 5 to create a diagonal win. By playing defensively here, I can prevent my opponent's progress while working toward my own winning position.