It wasn't my parents. It wasn't a life-changing experience. It wasn't even a choice. For me, believing in God is just part of life, something that I can't shake anymore than I can myself.
My parents were not religious. They raised us without any gods, or religion, or any spirituality, really. But I do attribute my belief in God to part of my upbringing: they chose to raise me in a fairly conservative rural area, in which we were surrounded by colonies of Mennonites, Mormons, and Orthodox Old Believers. When everyone around you acts like God is a given, I guess maybe its hard to not believe.
Going to a rural, public school, I was the only student I can recall who claimed not to believe in God. It was not true, but I claimed it, because I thought it was the case, and because the rest of my family didn't. It took me along time to realize that, in fact, all of that time when I'd been claiming I didn't believe in God, I'd always had a funny feeling when making the rational argument against one.
I was in denial. There was a kernel of belief somewhere, deep down inside, which I could not dissuade with any rational argument. For a while I thought: "Well, I believe in God, I just don't like him much". Frankly, now I'm much more ambivalent. I don't think God is like man. I don't think God is good or bad. I don't think God is there to be worshiped, and its useless to despise God, likewise.
To me, God is just there. And it is irrational. And I accept that, generally. I have some doubts, of course, because nothing is certain, but as I've said, I can't get rid of the belief.
Nor do I think it is necessary that I should. After all, there isn't really proof either way about god. It isn't being any more illogical to say that there is as that there is not a God. The existence of God is something that science cannot quite determine, by the very concept of God. How can one prove or disprove something that is by definition infinite, and therefore is beyond human understanding?
The God question is one of a few which cannot be answered by science. We are all true agnostics in this; any answer we provide is only a belief, not certainty. I welcome the ambiguity of it.
I should make clear, though, that I have little patience for most other beliefs that religions try to tell us are truth. While I may believe in God, and consider myself a Jew because of that, and much more importantly, my lineage, I am not faithful to any organized religion in all or even much of its beliefs.
Because of this, my belief in God is harmless. I don't have supplemental beliefs which make me hate others, or seek to convert other to my beliefs, I merely seek a place of my own in the world, where my beliefs are accepted as being as valid as anyone else's.