This is an eternal question for many folks. Kind of like; what makes a good husband? What makes a good friend? Everyone has qualities they're looking for and in the long term, you end up compromising some things you may not like because you know the good qualities supersede those not so likable qualities.
You decide what you know you can and can't live with. Of course, in buying a horse, you usually don't get to spend lots of getting-to-know time before purchase. Many times, it can be a shot in the dark or simply a matter of trusting your instincts.
I'm probably not the best person to advise anyone on horse buying. I would tell them to follow The Rules! Those rules found in articles about buying horses.
I didn't follow the rules when I bought my guys. I bought the first ones I went to see. I didn't get a vet check. I took my non-horsey husband (at the time he didn't know much about horses) with me, not my more experienced horsewoman friend. I'm the kind of person who tends to go on instinct. The little voice or feeling that says "yes, it's right" or "no, don't even think about it!" My instinct has served me well over the years and I trust it.
What makes a good horse for me? Well, most horse people would say "oh, she's one of THOSE...." because, I have to be honest, I sort of fell in love with Bo the moment I saw him. Love at first sight isn't always a good thing in many situations. My husband and I took about 2 years to get to know each other before I felt I was really "in love" with him! I guess in picking my horses, I found the qualities I knew I wanted right off the bat. I think I was lucky.
The wonderful couple I bought my guys from loved their horses and I could see it reflected in all their horses. They were well cared for. After talking to the couple for a while, I got a feel for how they handled their horses. They had raised them with affection and affirmation. The horses were what I term "people horses". They wanted to be with people and they would be willing partners. After only a couple hours, how was I so sure? You know, I still don't really know for certain to this day. What I do know is that my instincts and feelings turned out to be correct.
Now, my guys are not perfect but after reading tons of material, blogs, and email posts where people discuss their horses having one problem or another, I feel I was blessed! My guys really are gems.
Spirit lives up to his name sometimes. He is very sensitive. He's very intelligent. My husband asked me what I saw in him. I told him something in Spirit's eyes, though I have trouble explaining what that was exactly.
When he was presented to us at the seller's farm, Spirit ran full blast into the round pen, running around like a crazed horse and from there tried to jump out. He was a green two year old at the time. My husband thought I was crazy. I still remember the look of horror in his eyes. Kind of funny when I think about it now. Spirit calmed down, I went into the round pen with him. I stood in the middle, my head down slightly, not looking him in the eyes. He approached me. It was then that I decided, he had picked me as a leader. Probably something else going on Spirit's brain but that's how my mind worked at the time. I'd absorbed all those Natural Horsemanship lectures from Pony Boy to Monty Roberts to Clinton Anderson. In my mind, Spirit had qualities I could work with over the long haul. Hubby wasn't so sure. He still isn't sure of Spirit sometimes, but I am.
Bo was the opposite. He was 6 years old at the time. He was mannerly and obedient during the try-out ride. He was actually kind of balky. He can be stubborn, which I was told beforehand. Nothing I felt I couldn't work with. Hubby was definitely smitten with this one! Though Hubby later learned when it comes to riding, a balky, stubborn horse isn't as easy as he thought it would be. Live and learn! He's learning.
After four years, we're all well acquainted. I know their quirks. They know my moods. We accept one another. Bo chews on the wooden part of the fence when he's bored in the winter. Spirit still gets wild eyed when something startles him. Bo can be as moody as a boss mare, but I can accept that because so am I at times. Spirit paws with impatience when food is coming around. Bo will try my patience with his stubbornness during riding sessions, but if I patiently keep after him and encourage him he works with me. For a while, Bo didn't want to stand still while I mounted. I believe his previous owners didn't ask him, just jumped up and took off on him, so that's what he thought was expected of him. After a period of time, and more patience on my part, he has learned that I require him to stand still. Spirit used to move all over the place when the farrier worked on his feet, but now, he is as good as gold. He even stands for Hubby to do a little rasping in-between farrier visits.
I think to myself, if I ever had to sell these guys for some reason, would the person who bought them be as patient as I've been? I hope I never have to find out. When I bought these guys, my intention was to have them as partners for the rest of their lives. In my mind, in my eyes, they are good horses.
A good horse. Hard to define in simple terms. There are many variables. It's an individual definition and everyone's definition will hold up to the qualities they are looking for in a good horse.