Highly unlikely that anything the candidates will say is going to significantly change my opinion of any of them. There are vastly better ways to determine which of them is preferable on some combination of competence and policy.
My approach to the 2020 Dem primary is very similar to my approach to the 2016 GOP primary. In 2016, my view was that any of the other major candidates was vastly preferable to Trump, and therefore the thing to do was support whichever had the best chance of beating him. This time any of the other serious contenders is vastly preferable to Sanders and Warren. de Blasio may be comparably awful, but he has no real chance of winning, so I need not worry about him.
I have a tentative view that O'Rourke, Klobuchar, Castro, Delaney, and Hickenlooper are a cut above the rest on policy (each in slightly different ways). But I need not spin my wheels trying to figure out which of these is the best (or least bad), because it's highly unlikely more than one of them will emerge as a serious contender (if even one does).
In sum, all I really need to know at this point is that I'm #NeverBernie and #NeverWarren. In the hopefully unlikely event it comes down to the two of them, Warren is probably the lesser of two very great evils. But I don't need to think about it too much (at least not yet). Ditto for the awful possibility that the general election will come down to one of them vs. Trump - a scenario that might make me pine for good old days of 2016.