As mentioned, the earliest pretty much involve Sun worship.
Don't forget the Egyptians (i.e. and their sun god Rah...).
For the oldest/best documented, I'd have to go with the ancient Egyptians on this one...more than 3000 BC, and certainly long-lasting and
Hinduism is a close second on that....both in age and documentation.
Don't forget also, that the basics of Christianity, i.e. the Old Testament was all before Jesus...(though not as early as the above)
Most factual? That's largely a matter of opinion. I'd have to go with Buddhism on that one, as it's largely a philosophy, rather than strict
EDIT: Seems we were composing this at the same time, hehe....
I'm not as familiar with Dravidianism....but as the area was pretty much the cradle of civilization, it'd make sense....I just don't know how much
of it was actually well documented prior to 3000 BC...
The interesting thing one sees in comparative religion, is how much each religion was influenced by and incorporated the beliefs of others. For
example, many of the same people and places are the foundation for Judiasm, Christianity, and even Islam. The veneration of the sun and animals is
evident in the first religions, and you'll see this carried even into existing religions. After all, think of the animal sacrifice in the story of
Cain and Abel...
Rather than reading, if your local college offers a course in Humanities, I'd recommend taking one, or even a comparative religion class. Just an
[edit on 15-9-2005 by Gazrok]