I think that a person's accept reflects the local dialect of the people they grew up around, a child will quickly try to imitate their parents and other adults in the community and that is where the accent comes from, I don't think it has anything to do with the intelligence of a person.
I have seen people with no accents be some of the stupidest people I know, and I have seen people who you can hardly understand be some of the smartest people I know. How someone talks usually has no reflection of how smart they are. I do believe there is a stereotype that someone with an accent is smarter, but that is not true.
Accents really are only a reflection of where someone grew up. While some accents may sound more intelligent, like a proper British accent, may sound more intelligent, this is really only a bias that we have, perhaps from movies. There are some dialects that we associate with people being less educated, like Eubonics, but again, this is merely be a reflection of the environment a person grew up in.
A person can be a very intelligent person, but grow up in an area where people consider the accent "less intelligent". There truely is no more or less intelligence for an accent. An accent is just an accent no matter how you look at it. It's a way the people began to talk.
Your accent has absolutely nothing to do with your intellect. Your intelligence depends on your genetics, your upbringing, the environment in which you spent most of your life, and how well educated you are. This is a really silly question, but one worth asking, because a lot of people seem to believe it.