I love HN because I can find tons of high quality opinions/information about many different subjects I am interested in.
Therefore, my favorite HN post changes for what I am interested in which is highly time sensitive based on what I am currently doing. I highly recommend everyone to search for "hacker news <some_new_thing_(generally_technology)_you_are_looking_into>" when researching new things.
Example: I was building a django app in my spare time and I wanted to know more about django channels which allows one to create web sockets. I Google searched "hacker news django channels" and found 116 comments talking about it from other professionals when it was first released: item?id=11305869
"Options vs Cash" item?id=14505378
"Ask HN: Sell my startup for $14M because I can't raise $2M?" item?id=15314663
"First employee of startup? You are probably getting screwed" item?id=2949323
"How I Sold My Bible App Company" item?id=11032480
"Ask HN: Who is willing to work for coin?" actually a negative example item?id=14776408
Of course worth mentioning is the “comeback of all time”: item?id=35079
This ranks right up there for meP item?id=13241427
That, and the Great Putnam Comeback.
I've got quite a lot of good posts in my favourites. Hard to point at one in particular though.