Because Bengal cats are social animals who often don't do well as the only pet in a household, people often want to adopt two kittens at one time. It seems everyone has an opinion on what genders make the best pair - including us. We have always recommended two males or a male and a female, but not two females. But this opinion was based on anecdotal evidence - our experience - not research.
Upon looking into it a bit, it turns out that the College of Veterinary Medicine at the University of Georgia did a study on sixty pairs of spayed and neutered household pets and published the results of this study in an article titled "Gender differences in the social behavior of the neutered indoor-only domestic cat" in the July 1999 Journal of Applied Animal Behaviour Science. Before this study, all of the information gathered about the interactions of domestic cats had been done on feral cat colonies with entire cats. In cat colonies, females form groups and males roam solitarily from group to group. Males regulate their interaction with other males by avoiding them, and it was assumed that desexed cats would follow suit, but that didn't end up being the case.
The study analyzed 60 pairs of desexed cats: 20 male/male pairs, 20 male/female pairs, and 20 female/female pairs. The results were measured in three different categories: affiliative behaviors, proximity, and aggression. Affiliative behavior is cat body language that encourages harmony in the relationship. This can be approaching one another amicably, grooming one another, rubbing their head on one another, sniffing socially or blinking slowly - basically, a cat's way of saying, "I love you." Proximity is how much time the cats spend within the sight on the other cat. Aggression measured how often the cats had an aggressive encounter.
The three different groups of cats had no measurable differences in the affiliative behaviors or aggression. So, no matter the genders of the pairs, they were equally kind and equally disgruntled with one another. The one place there was a sizeable difference is proximity. Male/male pairs spend significantly more time within sight of one another than male/female pairs and female/female pairs. While we do not quite understand what causes this difference, it may relate to the fact that males do not spend much time in the proximity of another male in feral cat colonies. Therefore, male cats have more body signals to indicate to one another that they are not a threat. It is theorized that because males have more ways in which to communicate a lack of desire for aggression, this may end up benefiting them in a household situation.
So, if it isn't gender that affects these behaviors in spayed and neutered cats, what is it? It is mainly the amount of time spent together and the number of desirable territories that have the greatest impact on the harmony in a pair of cats' relationship. The number of aggressive interactions a pair of cats had with one another each day decreased with the amount of time they had lived together. As cats grow old together, they engage in fewer aggressive behaviors. When the cats did engage in aggressive interactions, it was largely based on territory. If there was one preferred resting spot, the aggressive interactions tended to happen most frequently around it. Bottom line, the more preferred resting spots you provide in your home and the longer your pair of cats is together, the more harmony there will be in the relationship.
In a nutshell, as spayed or neutered pets, gender does not affect the amount of harmony in the relationship, so you are free to choose whichever two kittens strike your fancy. Just make sure that you have enough desirable sleeping stations placed around your house to keep the peace.
Barry, Kimberly J, and Sharon L Crowell-Davis. “Gender Differences in the Social Behavior of the Neutered Indoor-Only Domestic Cat.” Applied Animal Behaviour Science, vol. 64, no. 3, 1999, pp. 193–211.