My favorite is the Vought V-173 (and XF5U). Also known as the flying pancake (or flying flapjack).

https://en.wikipedia.org/wiki/Vought_V-173

https://en.wikipedia.org/wiki/Vought_XF5U

https://youtu.be/LfpTDOAfj7Y

Simple structurally, awkward looking on the ground, slow takeoff/landing speeds. Because of takeoff/landing dynamics I wonder if it would have been a safer platform for small civil aircraft. Though who knows how it would handle losing an engine.