If this will be your only dog, I would get a female. I would get a male as a second dog if you ever get that far, opposite sexes do better together I think.
If you have concerns about what dog to get, I would pay a dog trainer to go with you. There are a lot of signs a dog will give off that someone with experience will pick up on after spending just a little time with the dog. The local Humane Society here has a yard you can use to spend time with a dog before you pick one.
In Atlanta, there's actually a trainer that helps people pick dogs for free. I'd gladly pay $100 for the service when I get my next dog though.