In my area, english showmanship is the same thing except you wear the traditional hunt seat outfit (show coat, show shirt w/ collar, breeches, boots, show helmet, and black gloves). The horse is braided (mane, forelock, and tail) and wears either a plain brown or black leather halter w/ same colored leather lead, or a snaffle bridle with reins flipped over the head like a lead.
For Saddle Seat, however, you are dressed in the traditional Saddle Seat attire (Derby hat, traditional Saddle Seat coat, a white show shirt, a colored vest and tie, Kentucky Jodhpurs, black gloves, and shorter boots). The horse has a natural (usually long) mane, forelock, and tail, and it is not braided. They wear the traditional Saddle Seat bridle, and you can carry a Saddle Seat whip. Sometimes there will be a follower with a whip encouraging the horse to really move out.
Riders aren't 16 and pregnant. Riders are 16 and arthritic.