This is a “what-if” question, so if you don’t wish to participate in good faith, please go elsewhere.
A Voice From Above tells you that you have been given the one-time power to make any already established religion reality for the rest of time. If you refuse to choose one, the power will be given to someone you do not know.
Which one do you choose?
I don’t mean to nitpick but what exactly do you mean by “Reality”.
If you mean what I think you mean then it’s a pretty hard one to answer.
However I’m willing to play when I get your answer
FSM. RAmen.
Can I only opt for a religious tenant instead of the whole ball of wax?
If so, I’d say, “Let everyone REALLY treat others as they themselves would like to be treated.”
That would just about solve every problem I can come up with.
Do we get an ironclad warrantee that nobody can subvert the original purpose of said religion to turn it into a warmongering goat-roaping child-marrying parody of the original?
If so, I pick Buddhism. Easy.
So I’m picking the “one true religion”? Will the chosen religion be revealed to everyone else, thus putting an end to all of the other religions? If not, what effect does my selection have?
Goat roaping?
Surely you mean either raping or groping
Greek mythology. So that way I don’t just pick one god, I pick ALL of them.
Okay, things might get a little messy, like when they choose sides in the Iraq war and so forth. But they can’t do any worse a job than we’re doing, the Iliad aside.
This would confirm my opinion of Gods - if they exist, they are rubbish at:
So in a fit of pique I choose Satanism. :eek: Serves God right. :rolleyes:
If I was in a good mood, I would choose Buddhism, because it definitely causes less violence. 
You pick the religion, and the universe is run as if the tenets of that particular religion are true. If the chosen religion has a heaven and/or hell, then heaven and/or hell exists. If there are multiple gods with different functions, then they are real. If the world sits on the back of a turtle, then so be it.
that’s religious “tenet” you dolt
You pick your own religion. I meant what I said.
Oh, I don’t know, a religious tenant wouldn’t be so bad, if all it means is the old geezer in the spare room is a bit of a god-botherer but doesn’t make too much of a nuisance of himself.
Otherwise, IMO, the mysterious entity in the OP is not offering me anything extra as far as I can see.
No one can subvert your choice, but it has to be all or nothing concerning your choice, not just a tenet or two.
Make me #3 (I believe) going for Buddhism.
Oooh, I choose neopaganism.
Wiccan
Though I’m tempted to say Scientology.
I’m standing behind Litoris and the Flying Spaghetti Monster. It’s a peaceful religion and it would take centuries of old guys sitting around with nothing better to do to corrupt it.
Do the most votes win? How much influence have ya got on the universe anyway?
Tantra. The religious literature would be awesome.
The Egyptian religion might be good. I mean, they have it all written down and everything. Get buried like this, put these inscriptions on your tomb & sacrophagus, and you’re set in the afterlife. Things aren’t expensive and difficult to make anymore, anyone could afford a good burial. Want a ferrari in the afterlife? Get buried with a miniature one! Don’t forget the yacht, the mansion, and the battlemech! Want servants in the afterlife? Get as many servant statues as you can fit! I have a feeling the details (do you have to be buried in Egypt?) might bring the whole thing down.
Hell yes, there would by actual flying saucers and stuff. That would be far cooler than lots of other things.