if all things were equal, I would vote for an atheist rather than a theist. An atheist has a firmer grasp on reality and more likely to make 'better' decisions on more factual grounds. if the atheist was useless and the theist was able to do the job then I would perfer the theist. Who ever can do the job best is the best choice, regardless of their religious (or lack of) beliefs.
The xians would tear an atheist US president apart. Their criticism without ground perhaps but it would still be enough to discourage some people for voting.
An openly Atheist candidate wouldn't stand a chance in the current political climate. There are just too many theists that will vote against them solely because of this fact. It wouldn't matter if they were spot on with all of their policy.
Would I vote for them? Well, it depends. If they hold the same political stance as me, yes! If the only difference between the Atheist candidate and theist candidate was their theology, then the Atheist would get the tie breaker. But if his policy was contrary to mine, I would not vote for them anyway because that are Atheist.
So while A theist may make let theology be their first deciding factor, I wouldn't. I must admit that I would love to have an Atheist in office though.
I would definitely vote atheist over theist because of a greater grasp on reality, unless the theist had extremely superior credentials, and assuming they're not prejudiced against people of other religions, that is, they're of the incredibly rare 'accepting theist' variety. Otherwise the vote's on the atheist-- things like Bush Jr's claim that God told him to 'strike down the Muslims' and Bush Sr's 'All atheists are un-American infidels' rant quite scare me. Thankfully, the president's mostly a figurehead and corporate lobbying interests really run the country, but still the threat looms. I do not doubt the destruction of humanity (or at least a decent piece of it) by religion-instigated war within the century or so.
A silly little fantasy of mine has always been to become president just through the 'God wants it to happen' justification, then reveal I'm actually an atheist and fix the whole world by actually doing something.
Obviously that's an unrealistic idea, but one can dream..
All I can say that current president of Croatia said he was Agnostic and it was a big scandal because people thought he was an atheist, so people had to explain what agnostic ment.
So, my suggestion is, don't tell anyone that you are an atheist until you become president, than drop the bomb :D