A cat's personality isn't really defined by their sex. I've had males that were calm and males that were hyper, and the same variety with females. If you want a calm cat, DO NOT get a kitten! I recommend that you take a trip to the local shelter and discuss it with the staff there. They will be able to match you with a cat with the laidback personality that will fit in with your home and family. Good luck! We'd love to see some pictures when you get your little angel.
I agree that a kitty's personality and energy level is not determined by sex, especially taking into consideration you will have her/him spayed/neutered at the appropriate time. Both are wonderful and loving.