It really doesnt matter, I am 5"3 and my horses are all 16.3+ like kitten val said its what you feel comfortable with whatever you do, don't go to view a horse and knock it because of its height which is what I did! Good luck
I'm 5'3 and I got a 15.1 hh horse and another that's 16.2-16.3hh. I went looking for a horse under 16hh but ended up with a horse taller!!! LOL it depends on what you can find, afford, ride, and body structure....marco is all legs and is narrow (the big horse) and ozzie is really wide and "thin-impeared" and he's the smaller one. They both feel the same to me except marco has elevated movement and ozzie is flatter.
I'm 5'9 and I fit on my 14.1h mare just fine (even with western length stirrups, my feet aren't below her belly). It's all about how round or not a horse is. A wide, round horse is going to take up a lot more leg than a light boned TB.
I agree with Kitten_Val, it's all about your own preferences, your riding abilities, and your weight. Another thing that I think is important is the terrain you'll be covering. A smaller horse might have difficulty getting a big man up a steep hill but have no issues on the flat.
As other people said it's about personal prefrance I'm 5ft 2 my mare is 17hh's and my old boy is 15hh's.. My sister prefrers the little ones she had a young riders horse that was only 15hh's it was so sharp and quirky but honestly beleave it needed to be like that to jump 1.45m courses!! Don't have any wish to jump that big on my mare but I must say the fences seem smaller on a bigger horse!!