I am 5'4", and I have a 15hh TWH that, in my mind, is just the right height for me. Only sometimes I wish she were just a little shorter so I could swing on bareback from the ground. If I stand on a two-inch platform, I can make it up there-- but not without.
ridden a couple of 16.1-17hh horses, though. I do look small up there, but I have long legs so it's not too bad. They are WIDE Quarter Horses, so I almost feel like I'm doing the splits! It's a big change from my narrow Tennessee Walker, and my riding instructor says that riding my horse is like riding a 2 X 4!
Here is a picture of my horse: DSCF2292.jpg