I am going to take a guess and say that the upper class are the biggest number of religious people on this planet because they have never expirienced hardships or what it is like to be desperate so they can basically believe in anything.
As a upper class citizen it is easy to be religious or to believe in a god with all that financial success because they could easily fool themselves into believing that all the abundance they achieve is a god given.
( Imagines a wallstreet broker praying before he looks at the NASDAQ percentages.)
I see the wealthy use religion to control the masses although they are hypocrites and really are educated enough to be an atheist deep down inside. I think a def on what you mean by religious would be nice here too as kris pointed out.
Although maybe the poor have more to ask god for and more often attend church to get an answer from god. I think both groups are religious but we often pray for things to change rather than things to remain the same.
Maybe the middle class are the most religious because they do not want to drop down to lower class and at the same time are trying to achieve higher class status.
I think it’s easier to believe whatever wants to believe in, certainly if one is well off to begin with, but this scenario is less prevalent because there are less wealthy people then poor and middle class. If just talking about which class, The rich can more easily believe in whatever they want to believe because they have that luxury.
I would say the middle class is the most religious. It seems to me if you add positives and negatives up of all the classes, the middle class is the most likely to believe and feel that they benefit from religion.
Now do they attend church the most? Its possible because the middle classes make the largest class altogether. So by sheer numbers alone yea, they attend church the most.