One indicator that Warren should be the Democratic nominee

Warren is the best veep choice of both Sanders and Clinton.

They can't choose each other and wouldn't want to anyway. Warren is a kindred spirit of Sanders and a natural choice. Clinton would chose Warren as a sop to Sanders' primary success. Of course, it turns out Warren would be more likable than Bernie in a general.

I wonder if Clinton begged Warren not to endorse Sanders simply to avoid awkwardness for choosing her as Veep.