Before you select one, let me explain what I believe.
I think the 4%s are the main reason for his success, thus cheating, but I definitely don't think he's doping. He lacks some of the key signs that are mentioned constantly on this board. #1: He does not display an inexplicable lack of exhaustion postrace. He almost always hugs his coach or someone else, supporting himself, prior to falling to the ground. #2: He is anything but lacking in consistency. He has been consistently running under 2:05 (excluding Rio) and methodically destroyed every field he's raced against.
If you think he's doping: please explain your reasoning and what kind of PED he might be taking.
If you think he's cheating: Is it just the 4%s? Without these, would he still be the marathon GOAT?
If you think it's all natural: Do you disagree with the idea that the 4%s have carried him significantly? How would he have fared against a WR-racing Kimetto without these? What parts of his training do you attribute his success to?
tl;dr
I don't think he's doping, but the cheaterflys are probably a big reason for his success. What do you think it is? Why?