Its popular to go for two boys or a girl and boy - simply because it's easier to introduce a boy to an already established cat!
Once you hit F5 or higher, they are all pretty much the same temperament wise - just more levels back to ALC!
It is better if you can do the intro while he is still young enough to bond without feeling the need to fight - that way they will be life buddies. And you have a better chance with introducing a female if that is what you want - The boys do tend to be slightly more laid back characters, though, so if you want two lap cats, stick with boys! (I know females are also / often softies, but they can be the more aloof of the sexes).
One mandatory requirement, now you have posted, is PICTURES!!!! Lots and lots of them......