I honestly think only Sanders can beat Trump, especially since the DNC is going to come out of the primary looking corrupt if Sanders doesn't win.
I don't think Sanders will beat Trump. He appeals to liberal and disenfranchised young people, but he's too far left to win independents and even moderates. The risk to the DNC is that if Sanders isn't the nominee, his supporters will stay home rather than vote for Biden. That happened with Hillary last time.
Biden, Buttigieg and Warren aren't going to be able to do it either.