I posted this question: Which Armor Class values should be used as Controls when making Damage Calculations? in an attempt to try to reify the Armor Class values I use when making DPR calculations for this stack. It was closed for being too opinion based, and I'd like to know what an answerable version of this question would be.
My assumption is that the experience of stack users who've played a lot more campaigns than I have (which isn't a lot, FYI) might shed some light on which AC values are more commonly used by DMs and (possibly especially) published campaigns; information which wouldn't necessarily be gleaned from simply reading each statblock in the Monster Manual. But at the same time, I think there's ways to discern between bad answers to this question and good answers, and if not, then what should be done with the question to get to that point?