People who haven't played at least half of the games in each series shouldn't be able to vote :p
(Edit: I haven't played MI3, so that's my loophole
)
For me, it's GK over MI head and shoulders. The GK games had stories which I was thinking about when I wasn't playing the game, and which compelled me to keep coming back to finish them. MI, on the other hand, gave me more of a "meh, I'll finish this when I have some hours to kill" type of vibe. I just honestly couldn't care less about the MI series. In fact, I'd say that MI isn't close to being the pinnacle of Lucasarts' adventure games (see: Fate of Atlantis, Grim Fandango, Full Throttle, Sam & Max).
