Elizabeth Warren = Where are her foreign policy bonfides? She has a personality that will turn off a lot of voters dems need to pick up. She fell right into Trump's trap over the DNA test, and I personally think she's done. She would lose pretty bad to Trump.
Bernie Sanders = Too divisive, looks extremely old (well, is old). I don't think democrats want to relitigate the 2016 primary. He refuses to join the party. He won the dem senate nomination in Vermont, then declined the party's nomination. He repeats himself often, and doesn't seem to understand policy too well/how he would pay for and implement his plans. I could see Trump easily beating him in a state like Florida (Bernie has complimented Fidel Castro and praised Venezuela).
Joe Biden = Beloved figure in the party. He has middle-class appeal that dems need to win states like Iowa and even Ohio back. People are saying he's creepy ol' Uncle Joe, but I think that idea will be shrugged off. Most people who know him, including people on the other side, say he's a spectacular person with much character. Could win general rather easily.
Amy Klobuchar = She should probably be the dem nominee, but can she make it through the primaries? IDK. She would defeat Trump. She should at least be in very serious contention for VP. She is a bipartisan senator known for working with the other side. She'll win her reelection handily this year. Smart, gets a lot of legislation passed (unlike Sanders). Would win general rather easily.
Cory Booker = I think he has an authenticity problem. Has lurched far left since Trump came into office for political reasons. Was previously more moderate. Could win general, but not best choice.
Kirsten Gillibrand = Talented politician, but some think she went too far with the Franken stuff. Also like Booker, she was known as more moderate, then Trump came in and she lurched far left for political reasons. There will be questions over that stuff. Could win general, but not best choice.
Michael Bloomberg = He might be seen as a carpetbagger. Plus like Bernie and Biden, is old. Could win general, but not best choice.
Kamala Harris = Could she bring the Obama coalition back together? There's no doubt she would do well in primaries with high minority participation (i.e. the deep south). Still, prob not the best choice for the general.
Eric Garcetti = Don't know enough about him, tbh, but seems intriguing. At first glance, he could do well in a general...but can he make it through the primaries?
Steve Bullock = I know less about him than I do about Garcetti.
Most likely to lose, i think, would be Elizabeth Warren and Bernie Sanders. Most likely to win: Amy Klobuchar and Joe Biden. Take it for what it's worth. Just my opinion.