Speaking from personal experience here... being knocked out is the absolute worst.
A loss by submission is very embarrassing, but think of how you've been submitted in a real fight. Has anyone really made you lick their pussy, or made you beg for your dignity? That stuff is really hot in a fantasy setting, but in reality it doesn't happen often.
When I was submitted by ex boyfriends current girlfriend it was terribly embarrassing to lose in front of him, but after I tapped out, it ended. She released me. What ended up happening was that she managed to pin my arms down with her legs because I made a mistake. From there she just moved into a more dominant position and I was forced to give. I almost felt robbed or cheated with how quick it was over. She won, but it felt like it was because of a silly mistake I made.
On the other hand, when my boyfriends ex knocked me out in another "fall" it was much worse. Sure knockouts can happen by accident, but honestly it seems like it's harder for a girl to land that "lucky punch" everyone keeps talking about. In my fight, as embarrassed I am to admit it, my ex's current girlfriend completely destroyed me. I underestimated her, thinking she was a just a prissy little bitch but she really took it to me and the fight was over wayy before the knockout. Actually, that's what makes the knockout so much more embarrassing. It's the icing on the cake for the winner. It's that final blow that leaves you completely and utterly destroyed and defeated, while your opponent is left standing over you triumphantly.
Their is no question of who won or who lost. It's clear and the embarrassment for the loser is inescapable.