Though one. I can't really choose. (That's partially because I always chicken away whenever I see a "religion battle" coming up. I just hope it won't happen here as killbill said.)
I'm not athiest, however, I don't follow any of the
existing religions. I'm kind of following my own very personal religion (but it is actually a bit of mixture between buddhism and christianity). I won't go too far into details because I just could write a book out of it and I'm not in the mood now.
The main reason I "made up" my own religion is because the
avaible religions are limited in numbers and precise in content, and unfortunately most of us (to some extend anyway) feel a strong membership in it... and that "group" idea sometimes leads to rivality and odd misunderstandings ; all of which I strongly disagree with.
Besides, I see religions as
propositions ; but in the meanwhile children often are too young to make such decisions, so the parents make the choice for them... but what will they choose ? Their
own religion of course. And after that, will they feel confortable to hear their child want to switch over to another belief ? -- That's more subjective, but I don't see much freedom of choice in here, or at least not smoothly.

So, what if you don't feel confortable in
any of those religions, aren't you allowed to believe in something just because you don't agree with any of the avaible groups ? That's what happened to me.
Anyway, I think religion should be individual, not a group's property. "Humanity" should be our group's label, nothing more. But well, it's unevitable, subgroups happen all the time, even uncounsciously (I myself feel a group-tendency just because I belong to the Aquarius' group..

)
I just keep that in mind whenever I see a discussion that lies on religion disagreement: "Thy shalt keep thy religion to thyself."