Thanks for the link to the list - I keep forgetting that exists. And thanks again to Andrew Hay for making it.
That said, I don't think I would say I learned anything from your OB posts, at least about rationality. I think I did learn about young Eliezer and possibly about aspiring rationalists in general. If that's a reasonable topic, then I'd have to suggest something in the "Young Eliezer" sequence, possibly My Wild and Reckless Youth.
There are several variations on the questions you're asking that I think I could find answers to:
"Which post do you think other people should read so that they will learn something?" (That might be the same as your third question) The Failures of Eld Science
"Which post did you enjoy the most?" Three Worlds Collide - if that counts as 1 post
"Which post do you recommend to people most frequently?" Zombies: the Movie
"Which post do you refer to most frequently in philosophical discussions?" Sorting Pebbles into Correct Heaps
It seems any 'favorite' type question will turn up fiction from me.
Philosophers are notably bad at following directions.
My current plan does still call for me to write a rationality book - at some point, and despite all delays - which means I have to decide what goes in the book, and what doesn't. Obviously the vast majority of my OB content can't go into the book, because there's so much of it.
So let me ask - what was the one thing you learned from my posts on Overcoming Bias, that stands out as most important in your mind? If you like, you can also list your numbers 2 and 3, but it will be understood that any upvotes on the comment are just agreeing with the #1, not the others. If it was striking enough that you remember the exact post where you "got it", include that information. If you think the most important thing is for me to rewrite a post from Robin Hanson or another contributor, go ahead and say so. To avoid recency effects, you might want to take a quick glance at this list of all my OB posts before naming anything from just the last month - on the other hand, if you can't remember it even after a year, then it's probably not the most important thing.
Please also distinguish this question from "What was the most frequently useful thing you learned, and how did you use it?" and "What one thing has to go into the book that would (actually) make you buy a copy of that book for someone else you know?" I'll ask those on Saturday and Sunday.
PS: Do please think of your answer before you read the others' comments, of course.