I've been asked this many, many times. Do you prefer a gelding or a mare? To beginner folks looking to buy I typically answer "You'll probably want a gelding but I hands down prefer mares..."
Mares think more. They are female, after all
Personally, I just get along with them better. I find some geldings to be rather annoying. I find that they seem to teeter on the edge of being so nonchalant (what everyone loves in a gelding) that they have too little personality for me OR that they are boarder line studdish and cause great disturbances in my herds. In addition (just something I've noticed over the years after working with many different horses, genders and breeds) the geldings stomp flies more, react to bugs on the trails and tend to be spookier. The logical non-stereotyping side of my mind says that's really not possible but the fact that I've worked with so many and taken note says its truth.
I own a stallion, two geldings and ten mares. One gelding is very smart, he takes fantastic care of his dam in the herd but is awful with everyone else. He is good for panicking about bugs on the trail, spooking when bored, busy behaving like a little boy in church and is stuck somewhere between colt and stallion mentality. He makes my stallion look like a total gentlemen at all times. The second gelding I wouldn't trade for the world. He's a great little fella to have around but when the first gelding isn't looking he will hop on a mare in heat and/or steal babies that he cannot nurse.
Mares on the other hand. I love them. In a "gelding free" environment once the pecking order is in place there is peace. No one is mounting anyone. No one is "herding" anyone. They have patience with the bugs and all look after the foals. On the trail when one of the mares are startled by something they will look, think and then just go. They seem generally easier to train for me. Faster learners. I have no herd bound horses, everyone can take a trail ride alone but when I train horses its the geldings that seem to want to give me the issues. "Not wanting to leave a new girlfriend" seems to weigh heavy on their minds.
As far as the tired and over used "mares are moody witches" saying? I've met a few genuinely awful mares in my day. Mmm maybe two. But a few rotten apples in the gelding and stallion genders also. Inevitable. For the most part I laugh at the moody mare statements, the only way you'll know my girls are in heat is when you see them peeing at the stallion. No misbehaving, "in heat" is not an excuse to a training issue. All in all I find the mares are sweet, quieter and simple. Like I said, IMO they think more. They also make great a GPS for when your lost. My mares always know where home or the trailer is, my geldings... one wants to keep riding and the other is running away from bugs
So, which do you prefer. And why?