I like a seat harness due to lower back soreness when wearing a waist harness. Just go with what you prefer. If a waist harness doesn't ride up on you and constantly drive you insane, maybe go for that to make toe side easier.

Hard shell waist harness with slider low friction ring for wicked toeside, no back pain and the ability to hold stupid power when riding the TT.

Fly on da wall said..
fine tune your stance n power rather than ride offset and rely on your rope slider to cover your poor ability to control your kites power and have good stance..

Huh what the hell does that statement mean?

Waist with slider. Sick for rapid alternations between heel and toeside.

For anyone whose waist harness is riding up - you probably have your kite too high too much of the time.
If your kite is too high it's probably because it's too big and having it high slows you down and gives some semblance of control.
If you want your waist harness not to ride up, try using a smaller kite - small enough that you can comfortably ride on all points of sail with it low in the window. For this, you'll probably have to learn to loop it without pulling the bar all the way in, so that the loop has as big a radius as possible and you get as much power as possible, sustained for as long as possible, to get you up and going in the lulls.