Which religion is considered having the most ...

"Blind belief" can also be seen as "faith."  It depends on one's point of view.  Personally, I feel that it can be inspiring for people to believe in something, in a day and age when belief is unfashionable.  As long as the belief causes people to be better human beings (more kind, generous, etc.), then I'm in favor of it.

I don't know whether this question has an answer.  But I do have a few thoughts about how to narrow down the possibilities.

The religion with the most observant believers would likely congregate in small communities.  The religion's adherents would be distinctive from anyone else who lived in or visited the community, based on aspects such as language or dress.  In addition, membership in the religion would require residence in the community (or another community of the same religion).

I have in mind a group like the Old Order Amish.  But perhaps somewhere there is a religion whose members are even more observant than the Amish.

There are more then a billion Christian believers who mainly dived between orthodox, protestant and catholic. Because they share many core beliefs and they use the same texts you can say they are all a part of one faith.

http://en.wikipedia.org/wiki/Image:Major_religions_2005_pie_small.png

I guess that depends on what you mean by observant.What really makes a man observant?Is it rituals ,chanting,robes and the other trappings or is it something inside that takes your faith and makes it the guiding star of your existence?I would say that true observance comes from a faith that transforms every aspect of your life.Such a faith will not be evident by appearances - but by how a person lives.How can statisticians ever quantify that?Good luck!

Religion is what a person believes in and God is not a religion but God is the creator and Jesus is the only door and your only Hope! religion does not rely on love, as God said you praise ME with your mouths but your Hearts are far from Me! there are only two choice's in life being in the family of God the Father and if your not then your father is satan the Devil  there is no in between! Life=Jesus the Christ; and life lost for eternity=Satan the falling Cherub!

As far as I know, Buddhism is the most observant believers, other than Muslim.  The true Buddhist forbids killing, steal, wanton/licentious/obscene, lies, drink wine/liquor, five so called commandments.

1. Killing -- not only killing human, animals or any living organisms intentionally or unintentionally, it also includes saying things that kill others' confidence, self-esteem, believe, ..., any word/speeches or actions that bring negative effect toward others... etc.

2. Stealing -- taking or possess anything that do not belongs to oneself, whether intentionally or unintentionally, example a pen, that normally will automatically goes into our pocket or bag unintentionally.

3. Wanton/licentious/obscene -- sexually conduct with the wrong person, for example not legally married opposite sex.  Not only non-marriage couples, even legally married couples are not suppose to make love in the day time, at the wrong place for example forest, living room, walkway, bathroom,..etc. The right place and the only place is bed.  In the view of Buddhism, the cause of homosexuality is related to one's constitution as well as from psychological conditions.  From a religious viewpoints, homosexuality cannot escape the item: contradicting morality -- having abnormal sex.  However, from the Buddhist point of view of cause and effect, all worldly sexual desire among men and women, men and men, and women and women contain cause and conditions.  The value of the Buddha's teaching is that the Buddhas and bodhisattvas understand causality very well.

4. Lies -- telling lies, saying thing that is not true.  Other than our daily conversation and salepersons' promotion lines, there are also misleading and fault report in the news media, giving negative effect toward the innocence.

5. Drink wine/liquor -- drinking and get drunk causing inappropriate speeches and actions, for example saying words that hurts other,  quarrel, sexually misconduct...etc.

As a general, Buddhism teaches the existence of passed and next lifes, cause and effect, negative action give negative karma and bring unforturnate consequences to current or future lifes.  These could explain why there are people borned to be unfortunate and some are borned with all the welfare that they could get.  Life is always fair and equal. in Buddhism, there is always an explaination toward any circumstances.

The scriptures only makes room for two religions.  The one with the most people isn't one of the world religions; it is the one which people belong to because their actions constantly dictate where they are heading and are constantly confirming where they presently are.  If you follow your lusts and your desires are constantly fulfilled you might want to question whether your on the most numerous religion in the world.  That  isn't where you want to be at the end.   

The religion with the largest amount  ignorent followers.