Suppleness is what's important to me in a tippet. Knot strength has never been a problem for me in any of them. And suppleness is real easy to test at home. Cut off an equivalent length of each material at equal diameters, put in vice at same spot, observe how it hangs, how easy it bends, etc.
Orvis Superstrong isn't supple at all, it's rather stiff. I don't think it's a copolymer, just straight nylon, like Maxima Chameleon. As such, it makes a fine leader material, just not tippet. In fact, I do use it in my leaders as a transition from Maxima to more supple tippet materials, it falls nicely in between in stiffness.
Of the one's I've tested, Rio Powerflex was in the lead for a long time. The new Rio Suppleflex beats it by a hair, but it's hard to find. Rio remains the king of tippets for me.
Fluoro has it's own range by brand, and ranges overlap, but it's generally stiffer than copolymers and more supple than straight nylon.