I have learned something while working for Rescue.

There is a very significant advantage to matching the gender of a new cat to the genders in the home already. Our rescue has placed close to 3000 cats and very much advocate mixed matches. Male and female. In addition to that, temperament is taken into consideration: Alpha, Laid- Back, Victim, Scardey, Passive are a few of the classes.

Through their experience, they found that two females close in age (within 5 years) is not a good match. Also, putting many (more than 3) males together can spell trouble (with marking, although neutered)

That does not mean that it never works out, it means the chances are less likely to have a happy household. Remember, cats form a heirarchy.
Some cats do not like any other cats.

I had a preference for male cats, until I added my third cat, Bella, a easy going female. I would definitely vote for peace in the house over my preference for males. Anyway, Bella, is my heart, my sweet baby girl, and she sold me on the love of females. So, now, it matters not.