I voted for "Unbreakable". "The Sixth Sense" used to be my favorite, and it's still really close for me between the two. But for some reason I find myself thinking about "Unbreakable" more and watching it more. It's by no means perfect, I think, but I just love the atmosphere and the way he builds the two main characters. In any case, I think they're both great movies.
I also enjoyed "Signs" quite a bit as well as "The Village" (though to a lesser extent). I recently saw "The Happening" and seriously asked myself if it was actually from the same film maker. I have no clue what he was thinking when he made that one, to be honest.
I haven't seen any of the others nor am I particularly interested, to be honest. I just don't find the stories and/or settings very appealing. I do really hope Shyamalan will one day make another movie like or as appealing as "The Sixth Sense" or "Unbreakable".