When one's book in sexual ethics is coming out (shameless self-promotion), one's thoughts naturally turn to the philosophy of science. :-) A standard line of thought is that naturalism is a simpler theory than theism in that it only posits one kind of entity, the natural world, while theism posits that and God.
A standard theistic response is to concede the point but say that theism wins out through greater explanatory power. Trent and I have, however, been exploring a different line of thought: One measures the simplicity of a theory (with "simplicity" understood in such a way that it is an intellectual merit of a theory that it be simple) primarily by looking at the simplicity of the theory's explanatorily fundamental posits (this has some structural resemblance to Huemer's work) rather than at claims explained by the theory.
For instance, suppose that according to our best physics certain laboratory conditions not occurrent in nature produce a Zeta particle. Alien scientists, who are the only ones ever to have the technology for this, are facing a great natural disaster they cannot avert that will destroy their civilization. As one last hurrah for science, they plan to produce a Zeta before the disaster. Unfortunately, at the last minute, they find that an extremely expensive part, which there is no time to repair, has only probability 1/2 of functioning.
Consider the theories: (S) They will succeed in producing a Zeta due to the part functioning and (F) They will fail in producing a Zeta due to the part malfunctioning. Theory S posits the instantiation of a new kind of particle that F does not. If explained phenomena also count towards the complexity of a theory, S is more complex. But that just seems wrong: S and F are on par simplicity-wise. Besides, if S were more complex than F, then if all other intellectual merits are equal--which they sure seem to be--then we should take S to be more likely than F. But that would violate what seems an unproblematic instance of the Principal Principle--F and S should have the same probability.
Or consider the Five Minute Hypothesis (5M) that the universe came into existence five minutes ago, fully formed, with fossils and light traveling apparently from distant but never actual stars, versus the Big Bang Hypothesis (BB). One might say: 5M wins out on simplicity grounds--there are many kinds of things it doesn't require us to believe in: world wars, Sumerians, dinosaurs, big bangs, etc.--but loses out on explanatory grounds. But I think that's conceding too much to 5M. BB is not only explanatorily superior to 5M, but it is at least as good in terms of simplicity--the explanatorily fundamental state of the universe posited by BB appears simpler than that posited by 5M: it doesn't include oak trees, dogs, people, continental plates, planets, stars, females, males (see, my initial self-promotion is on topic!) or galaxies.
But now go back to the philosophy of religion angle. On a filled out naturalism, the fundamental explanatory state is some brute physical facts, say the Big Bang. On a filled out theism, the fundamental explanatory entity is a perfect being, which then out of the goodness of its will causes the Big Bang. If perfection is a non-gerrymandered concept, then the theistic fundamental posit appears simpler, and so theism appears the simpler theory.
However, there is a wrinkle. I suspect that when counting the complexity of a theory one doesn't always get to completely discount the complexity of the explanatorily non-fundamental parts of the theory. Explanation comes in degrees. Deterministic explanations are more explanatory of the outcome than low-probability stochastic explanations. The Big Bang state is not determined by God's nature. So its complexity contributes somewhat to the complexity of the filled out theistic story. But given that the theistic fundamental posit is much simpler than the naturalistic fundamental posit, this may only make the simplicity contest a toss-up. Or at least it's now a much more involved question which story is more complex.