Well if authenticity matters to you, the most ancient and authentic, original Christianity is Orthodox christianity. The Catholics departed from the Orthodox church and then came the protestants. The Orthodox church practices Christianity exactly the way Jesus's apostles taught us. Which is why it is practiced by the countries who accepted christianity earlier. Countries to accept the religion first were taught by peter, thomas, paul and the other apostiles. Also, the bible was put together by the Orthodox church meaning the one true holy Orthodox church existed before the bible itself. Ik the other religions might also have something convincing or something that might make sense to you but, put this into account when you make your decision as Jesus IS God and wether we practice our religion exactly the way he told us to or not matters. (Notice how they dont have ye nseha abat in the protestant church when Jesus himself said "hidna rashn le kahn asay" to a person he just healed.) This is just one example... Ena good luck on ur research and may God help u make the right decision :)