Just supposing some theist were to convince that god/gods really do exist, I would be faced with a problem. Well, several little problems that are part of one whole problem.
You see, there are just too many gods to believe in, so many different religions, and so many inter-religious differences, that I would really need to try them all to see which one suited me best. But here are the little sub-problems:
1. Do I have time to try them all? To be fair to each belief system or method of worship, I reckon to give each at least six months before moving on to the next one.
2. Supposing I died before I had a chance to try them all? For example, supposing I had tried all the Christian sects, but it turned out the Muslims were right after all?
3. What if I died having already discarded the one true faith? Would I suffer eternal damnation for being an apostate?
4. What if I died the day before I was about to take up the one true religion? Would it be a case of "ooh, unlucky..."
There are also practical difficulties. For example, I don't think there's a Russian Orthodox Church or a Mormon Tabernacle in my town. I don't fancy have doors shut in my face during the Jehovah's Witnesses phase.
So, in conclusion, I think I'll stick with atheism. It's simpler, less effort, and more honest. At least until God, Allah or whoever visits me personally and tells me exactly he wants.