Personally I don’t think people need religion. I have too high of an opinion of human potential to believe that the majority of people need to live in fear of some supernatural punishment in order to keep them on the straight and narrow path. But if we did need religion I think that Zoroastrianism would be the best choice. Well, real Zoroastrianism is like any religion, over the years it has built up layers and layers of complexity and dogma, not all of which are desirable. So perhaps what I want to endorse is not Zoroastrianism, but a religion that borrows some of its central themes.
Let me describe this religion. Like any good mythology we start at the beginning of time, where nothing exists except a good deity and an evil deity. The two struggle, but since they are both omnipotent they are evenly matched, and thus neither can get the upper hand. To settle their dispute the two gods decide to jointly create the universe. They agree to leave the universe alone after its creation for a certain length of time. And after that time is over they will put all the good on a scale against all the evil. If there is more good then the good deity wins, the evil deity is destroyed, and the universe and all its souls fall into the power of the good deity. But, if there is more evil then the evil deity wins, the good deity is destroyed, and the universe and all its souls fall into the power of the evil deity.
Obviously this has the technical virtue of solving the problem of evil, but that is not why I think it is superior. Its superiority comes from abandoning the basically selfish core of traditional religions while still giving people motivation to do good. The selfish core I am referring to is, of course, the idea that each individual is responsible on their own for their eternal fate. This encourages a certain level of self-interest, because in the long run it doesn’t really matter what other people do, as long as you do more good than evil. And it also encourages a kind of cynical attitude about doing evil, where people feel that they can get away with a certain level of evil so long as they do enough good to “cancel it out” (or worse, that they can be forgiven for it without doing extra good), which is not a healthy attitude.
The religion I have described here avoids that problem by making every act of good and evil count. There is a lot of evil in the world, so doing just a bit more good than evil isn’t enough, you have to also work at balancing out all the people who do more evil than good. And it doesn’t matter how much good you do, every act of evil still helps out the evil side of the equation. Additionally, the idea that at the end of the universe the good and evil done by everyone is summed together helps promote the idea that doing good is a team effort. It’s not enough just to do good, it is important to encourage others to be good as well, and to stop as much evil as is possible. Thus it is harder for a believer in this religion to take a passive attitude towards disasters elsewhere, since their eventual fate is affected by more than just events that involve them personally.
Finally I would like to mention that this religion would also do a better job at giving people a sense of purpose and direction in life, something that is also occasionally pointed to as a reason that people in general might need religions. Most religions contain the idea that individual lives are all part of some divine plan, but what that divine plan is and how people are contributing to it is never revealed. Obviously that must undercut the message to some extent; it is hard to feel like you are part of something larger when you don’t know what that something is. In contrast the divine plan is made quite clear by Zoroastrianism: produce as much good and as little evil as possible. Nor is there any ambiguity about the role that individual lives play in the plan, everyone is responsible for tipping the scales a little more towards the side of good at the end of time.
But it is impractical to actually create a religion without actually believing in it, at least without deceiving people, and that would be unethical. More importantly I don’t think that people actually need religion for the reasons given. I think it is perfectly possible for every person to be motivated to act ethically and to feel satisfied with their life without religion, given that they are raised without religion. The transition from religion to no religion is, naturally, harder (as extra education is required to fill the role that religion used to), but I believe that many people could manage it too, if they wanted to.