Who's right, The Catholics, The Shia Muslims, The Ancient Greeks or The Pagans?

Just a brief conundrum for the believer, mainly fueled by the fact that in recent debates we very often see a non-believer on one side having to debate against, say, a rabbi and a priest. What always pickles me a bit is that the believing side can unite to give their point that "there must be a god because..." yet they're both talking about different gods. So, even if they convince the audience that there is a god, only one of them can be praying to the right god, with the other being deluded and praying to a figment of his imagination. It seems quite arrogant to be confident that your view is correct when some one with an equally passionate unfounded, non-evidenced  belief, held just as deeply as yours, is definitely wrong and deluded. The priest thinks the rabbi is going to hell and vice versa, there's no way around that.

Quite often when I voice my view that there isn't a god, people respond by saying "so you think X million people worldwide who believe in a god are wrong". Well firstly, yes, but secondly, if the Muslims have got it right, then X millions Jews, Christians, Atheists, Hindus, Buddhists, Pagans, Sikhs, Taoists, Aboriginals, Shaminists and Jedis are wrong and the ancient Egyptians, Greeks, Vikings and Romans were also wrong, and all of them praying to a god that doesn't exist, yet your god is the right one? To quote Dawkins "You're an atheist to every other god, I'm just taking it one god further".

Or to put it a little more bluntly, a follower of the Catholic faith can say that they know they are right as they have spoken to god and they have felt god etc and there's nothing that can be said to sway that. We call this the Bill O'Reilly response. Somehow this feeling is so strong that it is definitely more legitimate than the feelings of a Shia Muslim, who has also spoken to god and felt god so deeply that he's willing to strap himself to a bomb and blow himself and others up. If that man's delusions can be so deeply held that he's willing to go through that, can you really be sure your god isn't the delusion, or maybe that they're all delusions?