Voted for DM, as for D&D I call him/her like that, if I write something in english.
But actually, I'd call him "Spielleiter" or her "Spielleiterin" (which translates to Gamemaster, or GM), but that's mainly, because Dungeon Master sounds really stupid, if translated to german (and because we play some other games besides D&D and therefore it is more universal)!
I see and hear most often used DM, and that's why I voted it. Personally, I prefer GM - trying to break from the hack'n'slash connotation - but it just doesn't catch. So I just try to get called "Master" instead. Plus, it fits my megalomania just fine.
I really dislike "Storyteller". I can't really rationalize it, but I just associate it with a certain kind of elitism. Besides, as Flexor noted, "storytelling" isn't a good definition of what the GM does, no more than "DM" is.