We mostly have all geldings but I agree it depends on the horse and the personalities. You will get a lot of different answers.
Our show horse group is all turned out together, so we have a bunch of geldings turned out with a couple of mares. One of the mares is pretty much the boss of that group but they all get along well. Our horses share box stalls in the barn and I match them up with their personality and how they get along together and I have two "odd stall mates" a 37" gelding with a 28" gelding and a 38" gelding with a 31" mare but they get along perfectly and even feeding isn't a problem.
I turn out another 3 yr old gelding only with a one year old stallion who will be gelded soon. The older gelding does not play well with other horses (I don't think he was socialized at all as a baby) and if he is turned out with my other horses he jumps all over them and is constantly biting and bugging them and they tend to put up with his antics and then end up with bite marks and scratches and get really cranky. If that gelding pulls any of that with the one year old stallion, the stallion will not put up with it and will go after him and give it right back so they get along most of the time and the gelding is hopefully learning better manners because the stallion won't put up with his rough housing.
I also have a mini family that is pastured together, a stallion and two mares bred to him. He stays with the mares because he was pastured with mares year round his whole life and when I tried to separate him when I brought him home he was in an absolute panic and frantic to get back to his herd. One of the mares had a baby this year (our only baby) and the two mares and the stallion clearly share parenting duties and the stallion is very much the leader. I have found both mares asleep flat out on the ground while the baby is off with the stallion playing with him and climbing all over him. I was very worried about having a stallion, mares and a baby together but they are great and have a perfect herd dynamic going. If it is raining I've seen the stallion herd everyone in to their shelter and then stand out in the rain watching over them or acting like he is standing guard even though there is plenty of room for all of them inside. The baby will come out of that group when it is time to wean him and I will have to match him up with a buddy to keep him company. Maybe one of my more maternal older geldings.