My 2 cents, I think the seat harness is the way to go... check out the Dakine Nitrous.

Waist harnesses look good and are good for toeside tricks but damn they kill my back, legs and ribs. I am sore for days after riding.

There is a reason rock climbers use seat harnesses... and it's very similar to what happens kiteboarding. All load is at your center of gravity not your back or torso. You can edge harder for jumps and go upwind better with a seat harness too, and if you get the shorts it's one less thing to carry or forget at the beach. When overpowered you get pulled to your but, not onto your face.

The Nitrous shorts look just as cool as a waist harness and are comfortable..I can ride all day without being sore as long as I wear under armour (lycra sports underwear) to prevent chaffing from the leg straps. I can ride toeside with them, no problem you just twist a little harder.

Some still go for the waist harness. Personal preference.