I am about 5' 9" and own three shires(all are over 17hh) and a percheron cross that is roughly 16.2hh. I am interested in getting a smaller (anywhere from 15-16hh) horse and am interested in getting a gaited horse. I do mostly trail riding and pleasure carriage driving. I am not very familiar with the gaited breeds. Any suggestions?
I think you should probably look at Spotted Saddle Horses, Tennessee Walkers and/or Rocky and Kentucky Mountain Horses. Some RMH/KMH are under 15hh, but most seem to average about 15.1-15.2. Tennessee Walkers tend to be a bit taller, though as with every breed it depends on bloodlines and such. Spotted Saddle Horses are very very similar to Walkers in most instances. Personally, I would try several of each breed to see which gait you like better, they move in slightly different ways. As far as price goes(I don't know if this is an issue for you or not) RMH/KMH will probably be a bit more expensive in most areas, though Kentucky is a hot bed for both and they are much less expensive. While Walkers can also be expensive, there are a lot more of them around so not as pricey. One thing I recommend about RMH/KMH is don't automatically go for a chocolate, many people think that is the only color they come in. They come in all colors except spotted(separate registry). Chocolates may also be more expensive than say, a chestnut or black.
My two favorite gaited breeds are Rocky Mountains and Paso Finos. Both tend to be strong and hardy breeds and have heights that can be found in the range you are looking for. I also just like how they look compared to TWH and Spotted saddles.
However, you may want to not limit your height and actually try a shorter horse if they meet all your requirements in other ways. Some shorter horses are built in such a way they feel like a bigger horse. I'm 5'9 and I ride a 14 hand stocky haflinger and would like to someday find a paso fino or rocky mountain in the 14.2-15 hand range.
Rocky Mountain/Kentucky Mountain horses are often broke to both ride and drive. Kentucky Mountain may have more horses in the 16 hand range. However sometimes the taller the horse gets often the gait is less smooth. So much differs with the individual horse. That's why you must always test drive to see if the ride is smooth enough for you.
A gaited horse can pull a light load, but the diagonal gait has much more "pulling power" than the lateral gait (which most North American gaited horses exhibit). If you want to just do "fine harness" then they are OK. If you want to do real work you'll likely better off with something else.
I grew up riding Tennessee Walking Horse. They have a fantastic gait. I would not personally buy a horse that has been shown because they put such crazy shoes on them that they can get lameness issues from them. I am enjoying my Arab now, but my next horse will probably be another walker. I have one now that my husband rides. They can cover a lot of ground without jarring your brains out. Smooth and fun. The spotted saddle horses are usually dual registered as either Tennessee Walking Horses or Racking Horse Breeder's Association horses. A registered racking horse is biologically the same as a walker. The breed split years ago due to political differences. Racking horses are not shown at the canter. The first thing I do with a horse that is trained not to canter is to teach him that it is ok to do so.