Ortiz as he was rocked, maybe Dahapaus because it was the first time someone was able to take his punches without going down
I'm going to hazard a guess it was the one where allegedly he was knocked down, failed to beat a reasonable count, but was saved by the bell, which resulted in all trace of it being scrubbed from the internet.
Definitely Ortiz 1. Ortiz rocked him, and Wilder should have been down on the official cards (but wasn't due to extremely questionable judging). After that I would say Ortiz 2, Wilder lost every single round of that fight.
Dustin Nichol's.. when he was dropped with the check hook jab. It's a miracle he got through that fight in one piece. What warrior!