Not a bad lineup to be honest. While Biden is a bit of a conservative/moderate, he is still a left leaning one.
Now, I don't mean to rant, but:
I get a little surprised when I see Andrew Yang criticized as being a right-winger. This is clearly not the case as he is pushing for the most massive boost to low-income/no-income earners of anyone in US history. He's one of my favourites, probably 4th or 5th... I'll say tied for 4th with Castro.
I am a big supporter of Elizabeth Warren's no-more-corporate-bullshit approach - breaking up big tech would be healthy for the Western economy, and if Warren brings in the US Wealth-Tax then I can see EU countries following very shortly after. The big issue with wealth taxation in the past is that it is done in some countries but not others, and wealthy people can simply move their assets or accounts. I think an agreement across developed nations for a 2% Wealth tax would work wonders for public funding.
Bernie Sanders is my #2 pick, his policy positions are almost as good as Elizabeth Warren. What puts him behind her, for me, is that he tends to be very vague in what he is talking about, he lacks the precision of Elizabeth Warren. He's no more a socialist than Ron Paul is a libertarian. Bernie Sanders is a social democrat, just like Elizabeth Warren, which is a capitalist (and Ron Paul is/was a neoliberal). Normally, this wouldn't bother me at all, but people in this forum have actually tried to argue that he is a "market socialist" and have linked the wikipedia article - three problems with calling Bernie Sanders a market socialist: 1. Bernie Sanders has never called himself a market socialist, he has called himself a democratic socialist; 2. The core mechanic of market socialism still abolishes the capitalist stock market, which Bernie Sanders doesn't advocate; 3. Bernie Sanders favours big FDR-style social democratic government programs, which Market Socialism is against.
My third favourite is probably Cory Booker, he put a lot of people off recently with his support of nuclear power; but he was describing Thorium reactor technology (though he didn't use the word Thorium). Fusion reactors are also a potential for the future. But he is the healthiest seeming of all of the candidates, and so I trust his healthcare stance - he advocates local level healthcare improvements (which seems to be something the US is anemic on); healthy food, encouragement for exercise, pedestrian activities, etc... Since people have worried that donors giving to progressives will change their stances, Booker has proven otherwise in how he has voted against the interests of pharmaceutical corporations while also receiving donations from them. I don't think anyone is going to be corrupted by corporate donations, the problem with corporate donations is that they tend to heavily favour pro-corporate politicians, and that is why they should be banned: but playing the game (as Booker has done) and taking their money to work against them is something I support a lot more than the "refusal on principle" approach of Warren and Sanders (which I think is plain foolish).
I'll end my rant here.