I've had all boys, both from the same litter and adopted brothers and I've never had problems. I've also had girls but they were one cat situations. I've found boy kitties to be mellower but of course just like people all kitties are different. Could be I just lucked out with laid back boys! I've (THANKFULLY!) never had a spraying problem once the boys were fixed. I'd encourage an all boy situation but thats based on only my personal experience.