Well I voted other. When we speak of the general term for the person who runs the game we use GM/DM interchangably. However we never refer to that title when we speak to the person running the game. Even out of the game it's "It's Bob's game", not "Bob is the DM"
I try to be consistent - if I am talking about a person who is running a D&D game, I usually refer to them as a DM. If they are running something else, or I am discussing running games in general, I use GM.
I prefer "GM" to "DM." When writing things out, I use "GM." During our games I typically use "DM" [old habit I guess]. However, I loathe the term "Dungeon Master" -- it always makes me think of the D&D cartoon and this guy: