There are lots of types of stupidity and I've met plenty of stupid atheists, graduates, yes, articulate, yes, but stupid on a very profound level.

a (1) : the ability to learn or understand or to deal with new or trying situations : reason; also : the skilled use of reason
(2) : the ability to apply knowledge to manipulate one's environment or to think abstractly

I think atheists are more intelligent because they don't let fear inhibit them. However, do you become more intelligent when you let go of religion or is the potential always there?

I had a good friend who attended a Catholic seminary in England. When he graduated from HS and was to enter college he had to decide to sign a paper saying he would go on to the priesthood. He looked around and saw that those who signed tended to be the simple people who never asked questions. He had a lot of questions and felt he couldn't be a good priest unless he had answers, so he left the school.

I don't think they are necessarily smarter, however, they are likely to be freethinkers who question religious dogma. Religious dogma, in general, is a bit silly and anyone who can figure out that Santa is not real should be able to figure out that those religious myths we tell ourselves are equally fictitious. But religion does provide comfort, and a sense of community, and many people are unwilling to give that up. Furthermore, if we admit that it is not likely that there is a god, and most likely there is no afterlife, that requires one to face their mortality in a way most people would rather not. Most people do not think about things.

While I tend to surround myself with intelligent atheists and agnostics, I can't use that as proof that atheists and agnostics are more intelligent. It is just as likely I am surrounding myself with people that think like I do.

I think stupid people tend to be more biased and credulous.