The F-100 4A/4B is the worst joke in the industry. The exit row seat on the 2-seat side has more total space.

Take the MD80. If the flight looks like it's going to be light, take 21D instead of 21B, and you're likely to get all 3 seats free. 21B is better if the flight is going to be 70%+ full, as you're then likely to get somebody in 21E at that point.