Wow, some people have a lot of process huh :) I've basically gone by the rule "Do I enjoy this and want it so stick around in the future?" as my decision-factor to donate or not, so for the last decade or so I've donated about 5-10 EUR per project per month to currently 19 projects. I don't think I've collectively thought about those 19 as much as the author spent thinking about the selected three!

I have made large 1K EUR donations, maybe once a year, to various projects though, which of course takes a lot more effort and also logistics, like jumping on a call first with the maintainers and so on. But I think that's a different beast all together.