As you see everyone has a different opinion based on his experience. I was also wondering in the beginning how to find the interesting threads, now we are lucky to have the merit system and you can easily see the recent merited posts or other stats like the top merited threads for the last 120 days(?).
Other tactic is to follow some of the good forum members and check their post history.
For example browsing trough theymos's post history I find quite interesting topics and discussions, and if you want to be up to date with the current forum situation just check him every day