Rook over Bishop.
Every file is 8 squares long and involves both dark and white squares.
Most diagonals are smaller than 8 squares and only one color is involved.
I recently finished an endgame where my knight kept picking off my opponent's pawns while he couldn't figure out what to do with his dark-squared bishop since all my pawns sat on white squares. I'm glad he didn't have a rook.
Which is better in position, a rook on a file or a bishop on a diagonal? When you tell me your opinion, please leave an explanation.