Biden is the worst candidate of the bunch by that metric. His favorability is 17 points underwater right now, and he's losing to Trump in most recent polls by around 4 to 6 points. And keep in mind that that's measuring popular vote, not electoral votes. Hillary won the popular vote by 2 points and still lost the election. Biden needs to lead Trump by at least 3 points to even have a chance, it took a +4.5 margin to win last time around. And while we're comparing to Hillary, her favorability was only 15 points underwater in October after the Comey report.
Cornel West would be a way better choice. Even Dean Phillips would be less bad of a choice (y'know that whole "lesser evil" thing and all that). In polls, a generic Democrat leads Trump by 6 points.
But it's all a moot point because Democrats keep shutting down primaries and removing candidates from the ballot. They're attempting another coronation just like they did in 2016 - why would any candidate try to run when the party leadership is shutting them down?
So you don't think they should be able to try to vote on Ukraine aid again since the vote failed in the House?