which subreddits do HNers find the most useful ? I know there is many subreddit gems but it's not easy to discover them.

I love browsing those where I find excellent advices:

   https://www.reddit.com/r/awardtravel/ 
   https://www.reddit.com/r/financialindependence/ 
   https://www.reddit.com/r/startups/ (I think more human than HN for advices / feedbacks )
   https://www.reddit.com/r/books/ ( found great non-mainstream books to read )