I've always preferred female dogs. BECAUSE MARKING. With the ACD's, I was recommended to get the opposite sex of what I had because of SSA. A lot of times, I think the "gender traits" play into breed traits and the only differences between genders are boys are more goofy, and girls are more snarky (obviously a generalization). My notes:
Harlow: Not very biddable unless there is food. Even then, still on her terms. But, this is also part of the breed. Snuggles on her terms. Can be a snarky jerk.
Rider: Biddable until prey drive kicks in. Then he gives no shits. Very much so loves to be clingy, in your face, pet me until you go to your grave. Extremely worried about what his person thinks about him, and it can affect his drive. Good with other dogs.
Lucy (still a foster!): Biddable and soft. Much more handler oriented than I expected from her. A little less stubborn than Rider. Little bit of reactivity, and fights like a girl. Lol. LOVEY! Holy wow she is a lover. Not so much for snuggles, though.
In specific to ACD's, here is what my breeder has said:
Males tend to be more goofy, slower to mature, but their work ethic is strong, and then tend to be a little easier on the cattle (especially babies), and that they are "smarter" about the way they work and will try to fit their style to the situation. Girls on the other hand are more loyal, very hard workers, very gritty, won't show you their weaknesses, but tend to be less giving to cows and such. Also, girls tend to be less able to change their working style, and tend to go with "what works", even if that is a tad harder than a boy would start with.
Danielle is set on getting me to go with a boy, and I can't say I don't think about it (much better names!) but part of me just can't see not having a witch, gritty girl.