Which type of kiteboarding harness will give you the best ride?
This depends on a number of factors.
A waist harness is the oldest style adapted from windsurfing. It allows you to hold most of the kites power in your core, taking pressure off your arms when holding onto the control bar. This style is the most common one out there.
Common problems with a waist harness include it not fitting tight enough and riding up the chest. This can make it very uncomfortable and shorten your session by a huge chunk of time.
Seat harnesses are preferred by some riders that find that can't find a waist harness that fits and that enjoy the stance of the seat harness. This set-up helps some people to hold down the power more and get up on their board easier. Many schools use seat harnesses to help people at the early stages of learning.
The bent stance of a seat harness can be a bit limiting to those running up and down the beach and for wave-riding and freestyle. For many people once they get to be more competent and stronger riders they eventually will use a waist harness, unless they have chronic lower back pain which can determine which type they choose.
Vest harnesses are like an impact vest with a hook. With these the pull of the force is spread around your body and less focused on the lower back.
Shorts can have seat harnesses built into them. People like them partly because they look a little "cooler" than standard seat harnesses.
Important words - never buy before you try! Whatever you get, it's going to need to fit you well and feel comfortable. Some good brands include, Liquid Force, Da Kine, Mystic, and the Ocean Rodeo Session harness.
Lower back pain is a common problem for many people in many different sports. Depending on the type of back pain you have, you will probably feel a lot more comfortable in one type of kiteboarding harness than another. Or you might want to have two types to switch back and forth.
Here is a little more food for thought - take care of your body! Lower back pain probably means that you need to work on your core strength by stretching and keeping fit even when you aren't kiting. It will make all the difference when improving your performance.