Paganism in and of itself isn't a unified religion - the term simply refers to all non-Abrahamic religions. So while there are many pagan religions that are among some of the oldest known - "Paganism" itself isn't necessarily old, especially if it's being used more in reference to Neo-Pagan practices, rather than Recon Religions.
Other than that, of the current major organized religions in the World Hinduism is the oldest, dating back to 2000BCE, with Judaism coming just a bit later around 1500 BCE.
The oldest religion that is still practiced is Hinduism. Buddhism was based off of Hinduism. Daoism came around the time Buddhism entered China (it started in India). Islam is actually the youngest major world religion; it was started around 600 CE, around 600 years after Christianity started.
Let's see, ever since the beginning of time there has been temples built to worship God. The only church today that uses temples is the Mormon church or The Church of Jesus Christ Of Latter Day Saints. So I would say The Church Of Jesus Christ of Latter Day Saints is the oldest church because it teaches the same principles that Adam and Eve practiced and were taught by God himself.