Amicability. In the race for who people are really comfortable with on a human level, it's down to Uncle Joe and Mayor Pete.
It's important to remember than insofar as who is elected president, it doesn't matter at all who is smartest, who has the ideas most likely to affect positive change, who has been the most successful, etc. Look at every election ever: who do the voters like, as people? They vote for someone who is gregarious, pretends to be down to earth, pretends to respect everyone, and so on. It's simply a popularity contest, no more.
IMO it's more important to get Trump out of office than to get (your) "best" possible candidate nominated.