How do you decide which thread is worth commenting on before you write anything?

I posted the same comment in four different threads over a month. Same effort, same wording. The views were 221, 15, 12, and 9. The spread came entirely from which thread I picked.

That changed how I think about distribution. It's not a channel decision, it's a research step: how fresh is the thread, how many replies does it already have, does the original poster actually reply to people.

Do you have a way of predicting this, or is it trial and error for you too?