There is both truth and bias in what professionals will say, so keep an open mind while shopping for a horse.
A saying that might come in handy in your choice of whether to buy a mare or a gelding is that geldings are more like dogs, and mares are more like cats. That is to say, a mare might seem to have a little more going on mentally, and so might be more complicated, which might suit you—or not. Like all generalizations, this one has its place, but is, by no means, a hard and fast rule. Any horse should always be considered for its individual merits before its sex.
From the spring through the fall, mares have an estrus cycle once every month, which can make them unpredictable and moody for about a week during this time. If your pleasure horse has difficult estrus periods, you can simply keep a calendar of her cycles and consider not asking too much of her during these times, or at least be extra vigilant when you are riding her. If you are buying a potential show horse, this can be more of a problem, especially in the spring when her cycle begins again. Her ovaries, which are located just behind where you would place a saddle and sit on her, are acutely sensitive.
Veterinarian-prescribed medications can help to alleviate discomfort or pain associated with estrus. However, estrus temperaments vary from horse to horse.
Some even say that because of her extra sensitivity a mare can be more responsive than a gelding.
Horses with Sex
Another commonly held belief is that a horse with “sex,” which would also include a stallion, can have more “heart,” or “personality.” That is to say, a mare or a stallion might enjoy performing for you and competing against other horses more than a gelding.
However, owning a stallion can be extremely dangerous for the amateur horse caretaker and rider. When a mare comes in season, whether it is next door or miles away, there is little that will prevent him from getting to her. He might hurt you, himself, or other horses trying. Stallions are kept intact almost exclusively for breeding purposes, and so with few exceptions there is no reason to own one.
This, of course, varies from breed to breed and from horse to horse.
Some stallions of certain breeds tend to have very calm temperaments. “Cutting” such a horse might ruin his vitality and personality.
Geldings are generally considered to be more even-tempered, and so easier to train, ride, and care for. Most of the horses you will see at other farms and for sale will be geldings, and there is a good reason for this. Geldings will cause less trouble among each other during turnout, while a mare will cause competition and in-fighting among geldings.
A gelding might be stronger than a mare of similar breeding and size, especially if he is gelded late and given the chance to develop a stallion’s musculature. Some say that geldings are more dedicated to you, less distractible, more reliable mounts, and more affectionate than mares. As you will learn on your search, such generalizations are useful, but not always applicable.