I know they all slip up, but which model have you found best and why?
I have a flying objects, and its reasonable good, spreader bar could be a bit wider, but I got a cheapie, so for what it cost, its been pretty good. But wondering what people are using and why they chose it?
Cheers.
K
Pic unrelated.
Currently using a Dakine T5. Not sure why I picked that one exactly , maybe because they seem popular/no bad reviews, etc. Have used non sliding bars (Flying Objects) and sliding, not sure which I prefer as far as that goes but I find my T5 stays down for much longer than my previous FO waist harness and also feels more comfortable. I normally have both my older FO harness and T5 in the van Kurt so if you want to try either just ask.
I have only had 3 harnesses over the last 10 years.
A dakine surf seat which I thought was great then 5 years on a Pro Limit Rambler seat for slalom speed.
This year I decided to get back in the waves a bit more and went on a Guy Cribb course.
His advice was a waist harness around the hips with a longer bar that you could lock in buckle to buckle (no webbing showing).
I bought a Flying Objects Contour waist and was able to get a 30cm bar. I took out the quick release hook and just thread the webbing directly through the bar. It means that I have to step in/out of the harness but allows a really snug fit.
The hook sits at bellybutton height and barely rides up.
It is harder on the abs and back than the seat but I now use it for all my sailing including big sails and speed sailing. It makes transitions (hook in/out) so much easier than a seat harness and feels like it allows better trim of the board/sail.
Great Harness for me but I think it is all about finding the right fit. I definitely can recommend a wider than normal bar.
Thanks Evan, wouldn't mind! Next time I see you will give it a whirl 
Maybe after the race on Saturday?
lao shi - looking into a better harness for the same reason (Cribbs Clinic) - I felt noticable improvements with my harness further down and longer lines, more control and more "feel" if that makes sense..... so can see the right thinking of having your waist harness low and tight.
Mystic Warrior
Love it, never slips, doesn't crush your rib cage, really comfortable!
Pro limit "thrill seeker", never slides up and great quick release system.
Finally broke the bar last week after 3 years...
I switched to a pro limit "charge" seat harness, love it, lighter and less strain on the back
Go to a shop and try on as many as they have. There is a wide range and that is because people come in all shapes and sizes. No one harness is best for everybody. Even in the flying objects waist harness range there are a number of models.
Choose a size which has the minimum of webbing showing when done up snugly. Hook in using the harness loop at the shop and put weight in the harness to check for riding up and comfort around the ribs.
I bought the Mystic Code 01 6 months ago, the reason for me buying this one was back pain when I spent many hours on the water day after day. Back pain completely gone now! :) And...
No slipping also. Overall I really like this harness. I got the kite version, works perfect for windsurfing also, there's a windsurfing version also i you prefer that.
A great feature is the adjustable back support, you can adjust it quickly and easily on the water or wherever, just turn the dail until the support you want is strong enough. Only thing is maintenance, you gotta rinse it with fresh water the dial after each session but no prob to me, life long warranty on the system also.
The harness also has a kite line cutter thing which could come in handy if you surf in an area with a lot of kiters.
See the pic, top left is the cutter thingy built into the harness for you to use at you leisure.
Usually happens once its wet and I water start or beach start, the leg movement pushes it up...... 
As windxtasy says you have to try a few to see which fits your body shape.
On a Maui trip my gf went harness shopping and I thought I'd try a few at the same time. I tried about 6 or 7 brands, there was plenty of choice. Quality aside, half of them just didn't work at all.
I was sold an ION waist harness when I bought my first kit, slipped up so much it was a chest harness. It also had a kitesurfing hook, which widens at the end.
I would recommend Not using these, as a few times, I was caught under the sail, hooked in.
A twisted harness line doesn't slide off kite hooks, like a windsurf hook allows.
Anyway, I recently bought the T5 also and it hasn't ridden up at all, in 10 sessions. Very happy!
If you have a beer belly, then just fix it under it...wont slip at all... works for me haha
My thoughts are if you use very long lines as is the current fashion on a waist harness and try to drop your arse to get more down force and compensate for those extra long lines its probably not going to matter which brand of harness you use, they will all want to slip up.
Im old school 5' 10" tall and use 26 " lines on the waist harness and never have had the issue as I sail with my guts up and and keep my stomach muscles tight as Peter Hart recommends.
I have read somewhere that if you follow the Cribby theory that you will be constantly pushing your waist harness down anyway.
Im not saying dont follow the current trend as it obviously works for a lot of people but i also know of some very good wave sailors and slalom sailors that are not going super long on there lines.
I know I have probably gone of the topic a bit and in know way am I criticizing Guy Cribs techniques and teachings as I would not be qualified to do that.
Here's the way Peter Hart uses a waist harness in his faster dvd its more an upright stance and he is using his legs more and no way is is harness going to slip upwards.
