I know that Chaosium's Call of Cthulhu is essentially the official Cthulhu RPG, but I've also heard a lot of good things about Trail of Cthulhu (using the GUMSHOE system). They both seem to be well-liked but don't appear to be related mechanically, so I would like to know how they compare before deciding on one of them.
What are the main mechanical and stylistic differences between Call of Cthulhu by Chaosium and Trail of Cthulhu by Pelgrane Press?