I've tried a zillion different portable reflectors. Or at least five.
I recently found the Lastolite Triflip. Like many reflector kits, it is based around a flexible frame that starts with a diffusion scrim with zippered reflectors, white, silver gold and black. Like other reflectors, the Triflip comes with a stand clamp, and folds up into a transportable flat package, roughly 12 inches in diameter.
The big differences are twofold. The Triflip is roughly triangular in shape with a robust handgrip at the "point". If you've eve tried to handhold a reflector in one hand and the camera in the other, you know how awkward the larger round reflectors can be. The Lastolite Triflip is completely different. You can not only mount to a lightstand but also handhold the reflector and exercise excellent control of the reflected light.
When decent multi kits exist from a variety of fune vendors, we all have choices open to us. Since I shoot mostly on my own, and often am in situations where stands are inappropriate, this kit is really ideal.
Sell price is roughly $150 but I hit a sale and got the kit for $120. While I haven't discarded my other multi-reflectors, I carry the Triflip clipped to my vest, or daybag everywhere. For me at least, the key to useful kit it that it is kit you use.