I think all of mine (3) have been from Hell Meph. Don't presume that because forumites got things off a given boss that the boss has a better chance. It depends on how often that boss is run and what their drop chance is like. People run Hell Andy because her jewelry drop isn't watered down by higher level items. Besides that, I imagine many will come from Meph, since Meph is probably the most run boss in the game.
Hell Meph has dropped two of my best, but I don't remember for sure who dropped the other ones. In total I've got 4 or 5 of them. Only two has been saved because only two of my characters have found these charms. One with -14% vendor and 35% MF, other with -15% vendor and 26% MF. I usually look at the -vendor price, the MF is more like a bonus.