Biden seems to me like the type that people recognize and recall from the memes and Obama connection. But if you look at his record, prior campaigns or even his debate performances as a VP candidate...I don't see how anyone could sell him at the top of a winning ticket. Plus the civility stuff isn't winning any time soon. That strategy might play to very old people and "no progressives no matter what" types, but it'll lose the millennial enthusiasm for sure.
I still go Bernie...he actually tapped into something and the Progressive growth since 2016 is honestly shocking to me. His ability to win will get downplayed until we get closer to the elections, but the Republicans kinda handed him an easy pivot to any "he's gonna raise taxes on you" arguments with their tax plan gift wrapping so much money to the top earners (check the enthusiasm polls for the tax cuts). He can play off of that and talk about what the lost revenue COULD have been spent on aka his platform goals.
I think Warren's recent bills have good crossover appeal to bridge Centrists and Progressive Leftists too. But the native american thing has been attached to her heavy and hurts her.
Booker is interesting, I'm in Jersey and KNOW that this dude can campaign heavy. I also know that he's got some red flags but he may be able to break out of the pack off his prison reform and legalization stances which could garner a lot of support from the left.
Harris, I think some missteps in her past will be magnified in a primary with others. Doubly true for Eric Holder and To Big to Fail approach. I think they both make better VP candidates than top billing, especially for a more left leaning candidate like my pick Bernie.
I don't trust Gillebrand, but she does seem to have her finger on the pulse. She pivots on policy and marketing of her ideas faster than most and that's a big advantage going into campaigns. It also means that she's liable to do what's politically expedient first and foremost though, so I don't know how much I trust her to stick to any single path or vision. That said, the postal office banking thing is a pretty smart piece of legislation. She's another one I'd put as a better VP option than top billing.
So Bernie/Harris or Gillebrand is where I'd probably fall.
Warren/Holder could be interesting because I like how they approach speaking and crowd work.
Booker/Gillebrand is my bitter pill but I'll deal with it.
I think those combos all have a good chance to beat Trump, especially if they push their policy prescriptions to the forefront.