There's no rational argument to prove the existence of God. St. Thomas d'Aquinas' famous "God is that of which nothing greater can be thought" is, to my knowledge, the most rigorous attempt to apply reason to the subject of supernatural existence--but it achieves exactly the opposite of what it purports to achieve: it shows merely the limits of reason, rather than the existence of God.
This said, and as a consequence, reason can't provide any arguments against the existence of God, either. For that which can't be proved, can't be disproved either. (And, in fact, can anyone think of any law of physics or rational argument which disproves the existence of something? Non-existence is "disproved" on mere empirical basis--and it is thus never certain).
Therefore, the only rational (which does not mean necessarily: correct) position regarding God is agnosticism.