I trying to find a way to stay in a jet stream unpowered for a larger question. Is there a glider, kite or plane that flies best when in turbulent weather?
Turbulence is always a nuisance. It will require more control inputs to stay at the desired polar point, which increases drag. Also, small-scale turbulence will cause earlier transition of the boundary layer, which is important for gliders with a laminar airfoil. Powerful turbulence might even overload the airplane's structure.
Jet stream turbulence is low and only becomes noticeable at the boundaries between the fast moving air of the jet stream and calmer air above and below. To stay unpowered in the jet stream is impossible - any unpowered craft will lose altitude due to drag when moving through the air, and even a balloon will be hard to stabilize at the altitude of highest wind speed.
Even a kite is not unpowered - it needs some force acting on the line; either by an airplane flying below or by something holding the end of the line on the ground.
If you want to know what makes turbulence more bearable: Higher wing loading, lower aspect ratio and wing sweep will help. A higher wing loading means higher airspeed, so the relative speed changes from turbulence will become smaller. Both aspect ratio and sweep will reduce the lift curve slope, so changes in angle of attack will result in smaller force changes.