I prefer to call myself a Pantheist, or Spinozist, because it more accurately describes my beliefs. But if I was to choose one of the two, I'd say I'm an agnostic: I believe that the existence of an abstract philosophical concept like God is too complex to be understood with our current level of knowledge, but that doesn't mean that it should be assumed not to exist. I wouldn't say it's a 50-50 chance, or a millions to one as atheists say, but that we can't predict what the chances are. Does the Mandelbrot set 'exist'?