When I was younger and stumbling my way through disentangling myself from the religious dogma which had been hard-wired into me for the first decade of my life, I used to say (not out loud in my family) that while I didn't believe in God, I had to concede that it was possible that the universe was put in place by some extra-cosmic being. I grudgingly accepted that, by definition, any entity which 'started' the universe could be considered as a creator.
But the more we learn about evolution, not just of life but in terms of the way matter works, I find it increasingly hard to stick to that argument. I think I was still trying to come up with some kind of answer in case anyone I was asked by someone I loved but ultimately disagreed with.
Insofar as one person can make a decision (i.e. only for oneself) I can't accept that a rational universe contains an interventionist deity. As a rationalist I have to concede that without absolute proof I could be wrong - but strictly speaking 'absolute' has to encompass all space and all time so really no human being is capable of being absolute about anything. (1)
"If I were to suggest that between the Earth and Mars there is a china teapot revolving about the sun in an elliptical orbit, nobody would be able to disprove my assertion provided I were careful to add that the teapot is too small to be revealed even by our most powerful telescopes. But if I were to go on to say that, since my assertion cannot be disproved, it is an intolerable presumption on the part of human reason to doubt it, I should rightly be thought to be talking nonsense. If, however, the existence of such a teapot were affirmed in ancient books, taught as the sacred truth every Sunday, and instilled into the minds of children at school, hesitation to believe in its existence would become a mark of eccentricity and entitle the doubter to the attentions of the psychiatrist in an enlightened age or of the Inquisitor in an earlier time."
This is Bertrand Russell's famous "Celestial Teapot". Some claim this is a straw man argument in that it makes a meaningless comparison between a deity and a physical object. A deity is, by definition, not something which can be defined by the relatively simple physical parameters which can be used to define a teapot. Exactly the kind of convenient use of reasoning which always annoys me whenever I've tried to debate with someone of faith: if reason helps you to win, use it, but if it's helping the other side, resort to faith.
If God exists as an entity within the universe, it is therefore inside the universe and so the universe must be ever so slightly bigger than God in order to accomodate it. On the other hand, if God is bigger than the universe then the whole concept of a deity must exist outside the physical laws of the universe.
We are beings which are formed from and experience the universe through those same laws. So if there is a God, it can only be outside the universe and outside any possibility of us understanding what it is: not only must he move in a mysterious way, he must be way beyond things like movement and mystery. (Beyond even 'Life Jim, but not as we know it.') In other words, whether he's there or not there we can't possibly hope to perceive let alone comprehend him. So it comes back to do you want to believe or not? (2)
I can't see how, given the beings that we are, science can be argued to be fundamentally wrong: it's a way of systematising the collection and analysis of all the data we are physically and mentally equipped to acquire. I'm not saying that understanding everything is the single goal of life but it's not a bad collective goal for a species. It certainly seems a more constructive way to behave than to worship someone who, if he exists, seems to have done his best to make sure we can't get to him.
The optimist in me is pleased that we seem slowly to be evolving beyond this sort of guff. Like a dawning self awareness.
The pessimist in me focuses on how much human misery and waste has been created by something we outgrew long ago.
Here's a beautiful example of the application of reason to something which is not merely irrational but quite clearly bollocks:
 The Laws of Comedy state that at this point I should include a line such as "Except that Simon Cowell is a tw*t" but that's a little trite even for me.
 If you're trying to create a structure which enforces some kind of self-organising discipline on a society (the most positive view of religion I can offer) that's a brilliant starting point. It's almost the social equivalent of perpetual motion. Religions have historically used a vast range of sociological tools to embed themselves in human consciousness. Indeed, late in my school days, one of our teachers tried to haul us back in with this point (I think it's from Thomas Aquinas) knowing that most of us were probably drifting away from The Faith and couldn't be enthralled by demons and magic any more. Appealing to reason in some instances while denying it in others felt even then like a cop out, if not outright hypocrisy.