After a few months of deliberating, I've decided to edit this list somewhat. In my previous version, I noted that my list was cobbled together from various officially published lists, and the main difference here is that I decided to not use shows that only appeared in overly specific lists (specifically a "Best on Netflix" and a "Best of the 2010s" list), so it would seem less like I was scouring the internet for lists that included shows I specifically wanted. While I will miss those shows, the previous versions of my list still exist.
Here are my source lists:
https://editorial.rottentomatoes.com/guide/best-animated-series-of-all-time/
https://screenagewasteland.com/the-100-greatest-cartoons-of-all-time-100-91/
https://www.indiewire.com/feature/best-animated-series-all-time-cartoons-anime-tv1202021835/
https://www.menshealth.com/entertainment/g32380506/best-animated-series/
(I may update this list in the future if IGN ever updates their ridiculously outdated list)
Enjoy!