A better question should be how tall of a horse should you be riding. The horse should fit the rider but you do have to take into consideration what the horse is being used for. Horses that are big movers bred for dressage are usually tall as are upper level jumpers. A 6' 4" man doesn't look good on a 14.2 hand horse. A 5'2" woman doesn't look all that great on a 16.3 hand horse either and their legs do not bend around the barrel the way they should. If you have ever seen those three year old cowboys/girls riding around on dead broke ranch horses at team ropings you get the picture. When you are paid to ride horses you ride what you get and we used to train jumpers. Ripping the crotch out of my Wranglers mounting tall horses really got old. My philosophy is, if your legs are not long enough to mount without using a mounting block your horse is too tall. I am 5"7" and my horse is 14.3 hands, a perfect size for me. Size is an important thing to consider when buying a horse. As for me, I wouldn't want a horse over 15.2 hands tall.