I've had several Paradox Packs (which were given to me free for either articles or general testing, so caveat emptor), have built several of my own bags to use on the Paradox frame and belt, and own a Stone Glacier Solo bag which I use on an adapted Paradox frame.
I'm a massive fan of the Paradox belt and suspension system. It just works for me. Hopefully someone has used both and can provide feedback, as this is really the only important thing.
Build quality of the Paradox and Stone Glacier bags are both excellent. Both the Solo and most Paradox bags are quite minimal with few pockets, which I appreciate. I like and prefer the various xpac fabrics Paradox uses for their entire bags, rather than just the back and bottom of the Solo. The Solo's compression system is ridiculously effective, probably moreso than the Paradox, though I don't think it would make much of a practical difference. I've had no issue compressing the Paradox Unaweep down to carry a whole bone-in mule deer (and little else).