It depends partially on what you're sharing (and where you're sharing it).

Porn
  1. If it's a porn siterip, one megathread with one big post is what people are going to be looking for (and the link reporting bots don't give much of a fuck).
  2. For porn movies it's usually better to do one post per movie


TV Shows
  • Definitely at least one season per thread (one-episode threads/posts are crap).
  • If it's a dump site, you could do one show per thread--in a forum like the one I'm trying to build however it's one season per thread (also one host per thread) in the interest of organization and everything.


Movies
  • One thread per movie


eBooks
  • One post per series
  • Some forums do require one post per book; however, sometimes big collections can be a good starting point for new collectors, so some big forums will allow it (but only do Megathread if you have A LOT of books).


Games
  • One post per game
  • Exception: for collections that are small but with a lot of games (like NDS) SOME forums INSIST on Megathreads (others of us prefer a one-game-one-thread approach)