Why are you aiming at the atheists? Surely they wouldn't back any religion?
I personally think you should choose whatever religion or philosophy you are most comfortable with and which supports your own ideas about life and the world.
As an atheist I have looked at and into, (to a greater or lesser degree), Religion(s).
There is no single one which I would choose, given the choice.
If I could cherry-pick from religions and philosophies and build my own hand-book for living a good, decent, moral, non-judgemental, accepting of all life-style, I would..........and then again, I believe I already have, without recourse to any sort of God.
This is why atheists cannot answer your question with the brevity you seemingly require.
If by religion you mean a type of belief, then I'd say Pantheism. If however you mean organised religion, I'd maybe go for Quakerism (though Buddhism and Taoism are good too).
As a proud atheist, I have naturally given up all such nonsense and would no more go back to it than start believing in Santa again.
But answering the question in the fun spirit in which I think it was intended I think I'd pick Anglicanism - because it is the most harmless.
Roman Catholicism is deeply dishonest and rather sinister in the way that, like old Soviet Communism, it invents dogma and then insists that believers accept that dogma or be punished in hell, an idea that must terrify children. Its obsession with ancient bits of bone is yucky.
Jehovah's Witnesses would rather let a child die than give it the blood needed to survive, so they are beyond the pale.
Methodists and others forbid alcohol so I shan't toast them with my next G&T.
Jews are polite but the extremes to which they take the 'no work on the Sabbath' rule is just potty. (And what about Dawkins' account of how a very prominent Jew refused to shake hands with a group of women in case one of them was menstruatiing and would make him unclean?)
Islam is too dominating of a person's individualism and leads to behaviour (forced marriages, 'honour' killings and so on) which are unacceptable in real life.
Don't know much about many others, so I'll settle for the nice bumbling English vicar on his bicycle, saying nothing of much consequence and offending nobody, and probably not even a believer in God if the truth be known.