It may be because I've actually run very little CoC since moving to Brighton and have spent most of my time as a player, the vast bulk of it playing d20 games. I note right from the off that all of these were published in the last century. I've ranked them from tenth to first in order of enjoyment. In many cases I've run them more than once, and for beginners to Call of Cthulhu or indeed to first timers for tabletop role playing games generally. I am purposefully not going into great detail on each in order to avoid spoilers, so sadly can't comment too much on detail. Here's a list of what constitute the best scenarios for Call of Cthulhu that I've run over the course of over 25 years now of being a Keeper.