I take the middle road.
Just as the other hubbers have said, statistically, it makes sense, given the sheer size of the universe ( which is still expanding, after all, still evolving) so it cannot be ruled out entirely.
However, given all the conditions and coincidences that must be successfully met to produce life in the first place (the right distance from a star, a viable atmosphere, etc) I think it might also be somewhat rare. We may be the only planet with
(successful) advanced life on it in a great span of distance, like a lonely farmhouse with nothing to see for miles around but huge cornfields, if you know what I mean.
And by this I don't mean to imply some sort of creator or first cause, as I'm agnostic, merely the high rate of failure for life to become established and succeed in the first place.
So I will be more inclined to believe in other life in the universe, and more advanced forms of life, when I see more direct physical evidence of them. For now, I only believe in the possibility, but I would not go so fat as to claim certainty.