I've started conversations about this topic all over the internets, so some of you may not be interested in it, having already weighed in, but it continues to be something I think a great deal about. (Originally, I wrote a promise to keep this short. Sorry, couldn't.)
Backstory: I grew up conservatively religious, but my parents have never been overbearing about it, so both my sister and I were able to grow into our own spiritual persons without fear and worry. Our father, in particular, is someone who has been pretty candid about his own struggles--so struggle was clearly something allowed, and I continue to happily struggle through my process.
Where I would locate myself today: I call myself "agnostic devout." I do not know whether there is a god, but I have religious faith. In fact, I have religious faith to the extent that I have plans to go to seminary and be ordained as a priest.
The question of God's existence: At some point in college, I stopped having conversations about whether God exists because I found it to be an unanswerable inquiry that tended to be the place where good conversation about faith, religion, etc stopped. It didn't seem that this had to be the case, as seemed to be indicated by my experiences in Religious Studies.
The problem of "belief": For awhile, I stopped using the word "belief" without disclaimer. This has changed only very recently, as I've started teaching this confirmation class. The author of this wonderful book for teenagers (My Faith, My Life - Jennifer Gamber) discusses the word "belief," not as an intellectual action but as an action of the heart. Professing belief, in this author's opinion, is not professing knowledge but instead professing trust--giving over with one's heart to God. I (personally) do not need to "know" that there is a literal God in order to believe in this manner.
Stories: Over the years, I've come to have a very profound respect for our stories. I hear a lot of disparaging of these stories as lies, manipulations, or (at best, maybe) mere fairy tales, particularly in rationalist (i'm not using the typological meaning here) circles. In religious circles, I hear a lot of denial that these narratives that are so important in our culture are stories at all. We have come to demand that everything be factual, verifiable, falsifiable, "true" in one particular sense, and so Christians are forced to believe that Jonah was literally swallowed by a whale and literally spit out onto the shores near Nineveh, and rationalists are forced to deny that this story has any value whatsoever in our modern, scientific times. I have problems with both of these reductions of our stories (our... myths!).
We don't call nonfiction books "true" so that we can call fiction books "lies." That's not what we do. There are things that really happen, and then there are these other stories. The best works of fiction draw us into the world and have themes that apply to us. They have metaphors that "ring true" to us. Our myths are important because of their themes, not because they actually happened. Even if they did actually happen, they are still important because of their themes. Expecting a myth to be factual is expecting the wrong thing, in my opinion.
Myths are important. They're a work of human imagination, and they've guided (and continued to guide) our search(es) for meaning and purpose. That they are works of the human imagination, that they most likely emerged for evolutionary reasons, that they are not literally true--these shouldn't diminish them, in my opinion. It seems rash to sweep them off the table and replace them... It's like exiling the masterful works of fiction (which we love for a reason - they often speak to us on a level that other texts don't) and filling the library with only books that contain facts.
I think a lot of people struggle with what is authoritative, and I guess I just don't have that problem. Science is authoritative where we need it to be, history where we need it to be, the themes of myths where we need them to be. I just don't think we have to dismiss anything if we're willing to consider that there are different kinds of truths to reckon with.
Why I am a Christian: Given all of this, I obviously could be an agnostic devout anything. I'm Christian because it's my context. It's as simple as that. I could be a Buddhist, but what I love about Tibetan Buddhism is what it has in common with Christianity. It is my reference point, and I claim it as my own. So I'm a relativist/pluralist when it comes to faith, but I've taken my own stance and located myself in tradition--largely because I find rituals and community to be really valuable in my own life.