More of new-age / eastern spirituality. Cuz its all about meditation and attaining nirvana. No big meanie God to thump the Bible into his head. And no angry hopeless world view that this world is all there is and you are just like any other animal.
(um... look at the Bible deeply enough you find out that new age / eastern spirituality seems to miss out on something... *sigh* all these angry preachers make God look like a dictator...)
Well, a lack of gods anyway. Atheists can be religious and there are religions which are atheistic. But atheism isn't itself a religion. Nor is theism.
Islam is the fastest growing religion across the globe.
I wouldn't count atheism as a religion, though atheists are really increasing in numbers. So if atheism was a religion I'd say it was the fastest growing.