There are two worldviews: the one that establishes reality as all encompassing and has no need for the supernatural realm. This is the "rational" (within the bounds of reason exclusively) worldview.
The other view, the theistic view, asserts that reality requires a supernatural causation; thus, the supernatural --and less diplomatic sounding-- "irrational" (outside the bounds of reason exclusively) worldview.
And please note these conventions have nothing to do with the common ideas that a rational person is a well thought out person and an irrational one is a chaotic maniac. These are philosophical conventions, nothing more.
Both the theist and the materialist require some level or faith or trust (respectively) in order to believe their worldviews are reality. The theist's theological faith is an acceptance of the existence of a divine being who via supernatural means establishes all of reality including the laws of nature and logic which allow for the existence of knowledge.
The materialist relies on a priori logic that states that reality is self-caused, and empirical events allow for the existence of knowledge.
Both arguments have to assume their "bottom plank" cause exists in the first place in order to "prove" they exist in the first place. This is unacceptable circular reasoning for both, and both are equally victimized by it. Therefore, ultimately, neither side can appeal to their bottom plank in any true rational sense to support their claims.
However, we do live in a reality of some kind-- so in order to decipher what that reality is, we agree to put aside the ultimate paradox and work from that point upwards (though there is a third worldview which says we may be brains in a jar or the thoughts of an author and not actually exist at all, but even still the same agreement would apply). Therefore, the collective use of perception and the sciences can be harnessed to make sense of our environment, and as humans continue they show a clear trend towards doing precisely that. The sticky wicket here is that those tools may work in both a naturally-caused and a supernaturally-caused realm.
I conclude materialism because in my worldview, it does not help to add the supernatural to the overall questions of the penultimate-- in fact, it only adds an extra layer of mystery, and one that both materialists and theists alike agree precludes any answering (theists generally agree that their gods are "unknowable, incomprehnsible", etc). Materialists don't see why one would add that extra impossibility to existence, and while presently the materialist is burdened with problems of "what was before existence and how do we prove we know what we know?" it is not impossible to conceive a method would be discovered to put those concerns to rest. The theist admits that his incomprehensible god guarantees no such method is available to mankind (other than the self-asserted supernatural one, but even then, no human spirit or otherwise could attain godhood according to the fundamental Judeo-Christian paradigm).
Furthermore, I see no practical way to come from a rational perspective and assert an irrational one as the foundation. What happened "before existence existed" may be forever beyond us but that doesn't make it irrational as a concept -- it may be the "normal" state of affairs (just like the moment of time I just passed through may be completely beyond my ability to reclaim, but that doesn't mean it didn't happen in a natural way). God, however, is not only described by theists as irrational (outside of reason), but even as a concept is outside of reason (and I know theists will disagree with me vociferously on that point).
I conclude atheism simply because the paradigms offered by theists do not hold together for me (it really isn't any more complicated or diabolical than that)-- they are fatally flawed for one reason or another. For instance, the assertion that creation "clearly is evidence of god" ignores that "creation" and "nature" are indistinguishable in that sense, and if they are indistinguishable, no assertion that they are "created" holds value. This is the "coming upon a watch in the woods" paradigm, which ignores the fact that-- I know it is a watch because it is clearly and quantitatively different from a natural object.
Pray to your gods, worship them, hallelujah down the street if you want, teach your children about flying winged men in nightgowns, fat naked babies playing harps, chariots of fire cruising through the clouds, that seas part and books predict the end of the world, teach them all of these things if you want to, believe in them all if you must, but I find absolutely no reason to believe any of it.