My opinion on this is one entirely built from personal experience but here we go:
IMO, QHs are the best horse out there. Please do not bash me for it is my opinion but...
My first pony was a Quarter. The reason I say was is she was pts last August on the 24th. Worst day of my life. She was the most incredible little thing I've ever been fortunate enough to meet.
Her name was Baby. She was approx 14 hands. She lived only until fifteen because of Lou Gehrig's. Or ALS. She did EVERYTHING I asked but she was not deadhead at ALL. She had quite the personality :] Not a mean bone in her at all. She was incredibly clever and very level headed. I rode her on the road, in pastures, jumped her over EVERYTHING. Swam on her, did barrels, roping, cutting. She was so much better than I was at the western stuff I must say. I kind of just sat there and she did all the work. When faced with new situations, Baby just plowed right through with perked ears. No spooking. She was one of those little chunky QHs but very delicate at the same time. I miss her very much :[
The thing about Quarter Horses that I love so much is that they are truly a horse for everything. At my barn, we have a stocky little 15hand QH that does Hunters, Jumpers & XC. He's also dabbled in dressage. He jumps up to 4'3'' and currently he's 19 years old. He's slightly downhill, and he doesn't have the best conformation in the world, but gives 110% every ride to every rider who has faith that he can do it. And that's all it really is about every type of horse - body-build, age, breed, previous training and background aside.
I currently own two more QHs, a Peruvian Paso, a Belgian Warmblood, and a Spotted Saddle horse (and two mini donkeys, can't forget them :]).
At my barn, we have seven QHs - all ranging from thin and delicate to thick boned with big hips. 14.2-17hands. I love every breed of horse (except maybe Shetland ponies... once upon a time there was a satanic shetland named Butterscotch...) but QHs will always have a special place in my heart because they always try even when the odds are against them. Login | Facebook
^ my pony