It appears to me from reading this thread, quite a few people have their favorites and would pick them regardless of how the debate ended up. They could have had their head lopped off on stage during the introductions and people would still think they "won" the debate. Or they didn't watch it and had a predetermined pick.
Here's an outsider, objective view of the six participants from left to right on the stage to be fair:
Bloomberg: Grade D- Really didn't have a good showing, but went total Trump in calling out his opponents. He was unprepared and rarely discussed policy which was a good thing for his opponents since his policies aren't as radical as theirs and would have made sense to voters. They seemed to understand how dangerous he is and will become a threat.
Warren: Grade C Led the attack on Bloomberg, but is rearranging the deck chairs on the Titanic with her campaign. She's failing fast and hoped some cheap shots at Bloomberg would help her along. She talked some policy, but NBC is guilty of lobbing softballs over the plate to every candidate. No real movement except the 10 second soundbites that will be played for the next week or so.
Bernie: Grade B+ Didn't win or lose, however, Bloomberg calling him out on his number of homes and financial status was an indicator of how nasty this fight is going to be in the future. Do his supporters care? Nah, they knew it already and don't care an avowed socialist is doing far better than they ever dreamed of doing. He stuck to his message and didn't deviate.
Joe Biden: Grade D- He's failing fast and tried the adulting thing by not taking shots at his opponent. However, for a self proclaimed "fighter" there were plenty of opportunities to show the audience he's capable of taking the fight to Trump and winning the Party as well as undecided voters to his side. He passed on the opportunity. I'll give his campaign another month before he folds completely.
Mayor Pete: Grade B- He had a win in Iowa, talks good points, isn't willing to get as crazy as Bernie or Warren and clearly understands Bernie is the biggest threat in the room. But... his nice guy routine isn't going to win points with the base overall. He took his shots at Bernie, but did it in a "aww, shucks" kind of manner. He'll win a few things here and there and will make it to the convention, but cannot take the nomination overall. In short, he's the Marco Rubio of the DNC for 2020.
Amy Klobuchar: Grade B- It was clear the moderators weren't going to give her any slack and even be hostile to her over some things. She's also a centrist like Pete that isn't going to get crazy with the ideas and could gain traction with the moderate Democratic vote. Like Bernie, she stuck to her message and called out her opponents on some of their ideas. But can she move the needle on her campaign enough to pull out a top 3 win on Super Tuesday?
Biggest winner from last night? President Trump. None of the Democrats were tossing out anything new or groundbreaking that will resonate with the undecided voters. It was more "let's get rid of Trump" more than actual policies of why their plans would work better than what President Trump has done. Of course, raising taxes which will not resonate with voters.
President Trump is in the catbird seat at the moment and he just needs to stick to his accomplishments over the last 3 years and remind people they are better off now than before he was elected.