Hi Laurie,
I started trying out all three types and found that the integrated impact harness was by far the most comfortable for me. Does not ride up and I actually forget I am wearing a harness. I initially had back soreness as I was still new to kiting and my form was poor. Once I started keeping my back straight and using legs and stance to control resistance the pain went away(even after 4-5 hour long sessions)
BUT now I have found that to look really cool, all forward and back rolls and other tricks really need to be inverted and that is a lot easier with a seat harness as your center of gravity is lower so you don't have to whip the legs to get them overhead, just lean way back ane the legs rotate up. So now I alternate harnesses based on conditions. If it is really gusty and I am going to be hitting the water hard then I wear the impact harness, If the wind is consistant and I am looking to improve on rotations then I use the seat. Like any important piece of sporting equipment, you should go with what fits best. a small pain or discomfort will turn into a larger one after continued use(learned that with my first pair of Snowboard boots)