Buttigieg is the most articulate candidate I have ever heard. He's from the midwest and I believe he would be very strong in the rustbelt where Trump eked out his victory over a candidate who was weak in the rustbelt. He's actually "educated" and not just in the sense of schooling. I know that the online progressives don't like him right now, but I'm confident he could change their minds and bring the "progressive" and "moderate" wings together. He's not a phony. There is almost nothing from his history for Trump to attack him on. He served in Afghanistan and Trump is a draft dodger. There are almost too many things to list. I think he would beat Trump in a landslide. I think he is an elite-level candidate, even better than Obama/Reagan. NB As an apolitical person I would not support him myself. I am handicapping only.
Harris would do amazing numbers on the coasts and would be fine in some suburbs. I think Trump would win the rustbelt again without much trouble. I think her pandering style would turn off middle America. Basically a repeat of 2016.
Biden should be a tough matchup for Trump but time is up for "sleepy Joe". That's a brilliant nickname, the guy is too tired and unmotivated. Trump just has way more pep at this point and would undermine Biden repeatedly similar to what we saw Harris do last night until the voters get discouraged. Probably a lower turnout election.
Warren would drive suburban female turnout. It would be close due to Warren having some pep in the rustbelt. I see that as a very hard-fought battle but the 'pocohantas' attack would work better on independents and the youth than one might think. Keep in mind that incumbency is a proven significant advantage, so even though Warren is superior to Clinton in the rustbelt Trump should also perform somewhat better. (I am not as convinced as you that 2018 results will be predictive here.)
Sanders...his biggest weakness would be the "socialist" smear. It works even when the candidate doesn't call himself a socialist, and I think it would work even better here. "Crazy Bernie" is a brilliant nickname too. However: 1) Sanders is the most genuine major candidate in the entire race 2) His #1 issue is health care, which is a top issue for independents 3) He has showed serious strength in the rustbelt (consider his upset over Clinton in Michigan) 4) He polls extremely well against Trump head-to-head (usual disclaimer that it's too early for that to be predictive in many cases) 5) His anti-corruption, anti-greed message appeals to independents and disengaged voters. 6) He would turn out the youth vote. This would be dogfight. I don't think I could call it, but gun to my head I take Trump in a squeaker but I am not confident in that one.
@Oblivian what are your thoughts?