For my speed run project I decided to go with e2m6. I was drawn to this level because it takes advantage of a glitch in which the player escapes the boundaries of the map and walks directly to the exit.
The glitch works because this one of the only spots in the game where two walls meet at a 45 degree angle, as seen in the image below. This somehow makes the boundary weaker, and the player can SR50 outside the map if you ram doom guy at the perfect angle in the 45 degree corner.
Once you are outside of the map, you can view the monsters (see gif at top of post). Interestingly, they cannot see doom guy, and only react to the sound of his gunshot. Doom guy cannot kill any of the monsters from outside the map.
After you have explored the outside of the map for a bit, and are ready to complete the mission, you must hit the exit button from behind the wall it is situated. This is by far the most challenging part of the speed run. At first I spent at least 5 minutes every run trying to click it and eventually found quicker methods, though it still can take me up to 2 minutes to successfully push the button.
Overall, this level is fascinating to speed run because it exhibits the doom communities ability to share knowledge about exploits and build on that knowledge to find a successful speed run.