All indicators have pros and cons. Deaths by date of death is the most lagging indicator, which is bad for in-the-moment decision making, but it is also the most direct measure of the thing we should care most about, minimizing death-causing infections. So you can look at a graph of deaths by date, and if it is way down (like it is in Colorado right now), then you know that things were going well over the last few weeks. This doesn't give us any data on how well we're doing now, during our partial re-opening, but it will give us that information over the next few weeks, in a way that we can compare with what we were doing over the last few weeks.

Cases by onset date is pretty good too, but there is this period of some unknown number of days where it is misleading because it is too incomplete. The Colorado tracker shades ten days as "potentially unreported cases", but I always wonder how they chose ten and whether that's conservative or aggressive. The death by date of death has the benefit of not being incomplete in that way. Another problem I see with cases by onset date is that I don't really care that much about how many cases there are, not directly. If there were a huge number of cases, but no deaths, that would be a bummer because being sick sucks, but it would not justify our extreme reaction. What we care about are the deaths. So I like direct measures of that.

Cases by reported date doesn't seem very useful at all, for anything. Percent positive tests by day is a similar measure that seems more useful.

But I'm an amateur, this is just what I think is and isn't useful for reasoning about what's going on.