I would choose the tickets in Section 4 Row 41. Section 20 is nearly behind the stage and the angle of the seats direct you toward the middle of the field so you will not be able to look straight ahead to see the stage. There also could be potential viewing obstructions in your way on the side of the stage that would make it very hard to see. Section 4 has a similar angle but it not as far behind the stage so you will have a good view and you will not have to turn to see the stage.
Even though Row 41 in Section 4 is higher up and farther from the stage than Section 20 Row 33, the better angle and perspective make Section 4 more desirable.