I analyzed the board and noticed that the most forcing move is to play in column 2. Dropping an O in column 2 lands in row 3 and forms a potential diagonal with the O’s already at (4,3) and (5,4). This sets up a threat: if the opponent ever drops a piece in column 1 (to fill the gap), the next available spot in column 1 will be row 2, which would complete the diagonal sequence (2,1), (3,2), (4,3), (5,4) and win the game. Moreover, if the opponent avoids column 1, I can build a horizontal threat along row 3. Given these dual threats, column 2 is the best move.