I thought of a criterion when scrutinizing religions. It's a way to compare the belief systems of any religion in a way that helps determine if that religion's beliefs are right for me when compared to atheism.
Step 1: Get rid of fear
When considering any religion, I believe the first step should always be to completely take away any of the fear that the religion uses to sway believers into it. So if the religion is Christianity, take away the concept of hell to allow you to more rationally think its beliefs through. This is important because like it or not, in religions like Christianity, the fear of going to hell looms over all who are exposed to it as a subtle blackmail, and this fear can make even the most rational people aberrant. Just think of the things you would do if someone kidnapped a loved one of yours and was trying to extort you. You'd probably do things you thought were unthinkable. So completely remove any fear of the negative consequences of not believing the religion as a starting point.
Step 2: Consider all of the religion's morals
Now that the fear of hell is removed, think of the religion's moral principles. Ask yourself if you actually agree with them - all of them. It is careful to examine all the religion's moral values and not just a selective modern interpretation of them. Ask yourself if they make logical sense, and if they're actually practical. Are there any moral precepts of the religion that you feel would actually do more harm than good if implemented? Also, it's important to consider of how the religion's moral values were historically believed and implemented and how they evolved.
For me, my greatest exposure to religion was in the form of Christianity. So when I look at Christian morality, I consider many of its general ideas like the golden rule, caring for the poor, not being too greedy, respecting one's family and neighbor etc, all things most people would agree are decent and good to follow. But then I also have to consider the morality I deeply disagree with, like slavery, indentured servitude, loving one's enemy, the barbarous Mosaic marital and family laws, the idea that thinking is the same as doing, the idea that sex should only take place within marriage and only to reproduce, the idea that homosexuals choose their orientation and that they along with witches and adulterers need to be put to death, the inferiority and subordination of women, and perhaps worst of all, the masochistic idea that we're all born with original sin because we're all collectively guilty for the sins of two people (whom many Christians today do not believe even existed).
For me to accept these morals as being true simply because they are believed to have come from god, I feel would lower my integrity as a rational human being. And this puts a huge damper on my ability to reconcile myself with Christianity. Furthermore, the idea that morality, or objective morality, is dictated by a god through various people who declare themselves "prophets", I also think it does not help humanity one bit with the moral struggles we will always have. If something is morally good or right, it must be comprehensible to any rational person; its goodness also must be evident to anyone scrutinizing the moral principle and its effects on society. If that is so, we don't need god to come to know moral truths, or to ground them - they'd naturally be good or bad in and of themselves.
Step 3: Ask yourself if you want what the religion is offering
The next criteria to consider, is whether you actually want what the religion is offering. If heaven is the ultimate reward of being a part of this religion, ask yourself how plausible this idea really is and what is it actually like. Is heaven a place where you get to do all the things you weren't able to do in your earthly life, or is it some place where you are just showered with god's love for eternity? In the latter, there is no free will, no free speech, nothing to learn or achieve on your own or to dedicate your life to helping - nothing but being a mindless robot eternally suspended in the glow of love. Remember that's eternally suspended. It would be like being on the ultimate dose of ecstasy and just being insanely happy forever. And so I ask myself, what could possibly keep me interested in such a catatonic state for eternity except by being divorced of my memories and my personality and being turned into an automated robot? For me, my memories and my flaws are a part of who I am, they make me me, and so I decided that I didn't like that concept of the afterlife. I didn't want to spend eternity as a mindless drone.
There are other descriptions of the hereafter for you to consider.
Perhaps, like the Mormons believe, you want to be able to rule over your own planet in the afterlife, or like the Muslims believe, you want to go to a beautiful lush oasis where rivers flow with the tastiest wine and there are beautiful women all for your taking. (This idea of heaven obviously has greater appeal to one gender.) Maybe you want to be a part of an endless cycle of rebirth and reincarnation as some Buddhists believe. Or perhaps like me, you want to just die and cease to exist physically and mentally, and are fine with just being a complex arrangement of matter. In the end atheism offers me what I really want: finite existence.
Step 4: Do you like the worldview that this religion is proposing?
Next consider the metaphysical worldview the religion proposes. Do you want to be the special created object of a another being, to exist ultimately as nothing more than a means to its end, where you will never ever have sovereignty over yourself? Perhaps you do. Lot's of people do. For me, the whole idea sounds a little too much like living under a celestial dictator. But perhaps you like the idea that the universe was created with you in mind, or that events that happen in your life were created with a purpose for you. Although many theists think the naturalistic world view is depressing, I find it uplifting. I am made from the star dust that was forged in the hearts of stars and exploded out when they died. I am a part of the universe that is able to be conscious of itself, 13.7 billion years in the making. When I die, my atoms will get recycled for trillions of years and will perhaps even become part of other life forms. To me, this fact is as beautiful and poetic as any great work of religion.
There are however, other alternatives. You can like many people today believe in some sort of higher power that is different from the god spoken about in any religions, and this power or force you can believe has whatever attributes you think should apply to it. You can remain a doubter of all claims - theistic and atheistic, and be an agnostic. You can remain an agnostic and adopt a secular humanist ethos to live by. You could declare yourself an atheist by saying "I don't believe in god because there is no verifiable evidence for such a being." If you're sitting on the fence, there are lots of options available to you, and so I would recommend considering what effects the moral system you adopt (or already have) will have on society and the environment as a whole.
Betting on religion
To bet on a religion or a deity as Pascal's Wager induces us to do out of the possible consequences of not doing so, is to essential believe based on fear. And so in the end, the only reason I can think of for joining any religion is solely out of fear. Many theists think doing this reduces religion to mere fire insurance, and I would largely agree with them. If one joins a religion, it should be done without any fear and be primarily based on the sincere appreciation of it's beliefs and principles. For me, no religion offers such a comfort, and so I remain an atheist. But, everyone is different.