Elizabeth Warren seems like the best candidate for President so far. She is the only one (well, maybe Bernie Sanders also) who seems to have real plans in place for the changes she wants to make.
While I agree that Buttigieg has great abstract ideas on how he wants to move the country forward, and he does speak to the middle of the country, I don't think he's putting forth any specificity the way Warren and (his somewhat hero) Sanders has.
Beto, the more I look at him, seems like a clown. I think he's more about ideas or movements less than he is about actual policy. The only thing he has really talked about is that our immigration needs reform. Well, duh.
Kamala Harris is extremely intelligent but again, I'm not sure she's there in terms of policy. I think she could be a great AG, given her background, but that's probably not where she wants to go.
Biden, I don't think he moves the country forward. He's not bad, but he's not really progressive.