Seat Harness, Waist Harness or Short Harness?

This is a question I am asked a lot, and I have all three, so I guess I can express my opinion on them.
Seat harnesses are great when you are a beginner, they naturally push your hips forward, and they make you feel quite secure.  That secure feeling turns into a constricting feeling when you pass from beginner to intermediate.
I stopped using my seat harness one I started to ride toeside, as I found that it didn't let my hips rotate as freely as I would like and the harness felt in the way sometimes.  Having said that, I had worn that seat harness for over 18 months with no problems and it helped me to learn how to kite, so there is a place for a seat harness.
Now I ride mostly in my waist harness, I find it comfortable, it gives me freedom of motion in my hips and lets me crunch my abs on jumps.  I ride the Maui Magic harness, which is the same as the Mystic harness for the guys.  It has soft padding, and an extra harness strap to make sure nothing loosens during your ride. 
My short harness gives me similar freedom, however I have found that I can't wear them for as long as my waist harness as the short harness starts to dig into my hip bones.  I should state that I am a female and my hip bones do protrude quite a lot, so this might not  be a problem for the boys.
I like the softness of the waist harness and the back support, and so that is my harness of choice.
If you are a beginner, a good seat harness will get you up and started and keep your body position in check.
If you ride in warm conditions, where you don't need a wetsuit and wear minimal clothing, short harnesses are great.
If you are an intermediate rider or above and would like some back support, a waist harness with lots of padding is my suggestion.

Hope that helps :)