To be precise:I also think that Superfly is not as advanced at this point in time as iRay, there certainly seem to be more iRay shaders on sale than Superfly.
there are only a handfull of Iray shaders on sale, shaders as in different node trees or different MDL files. There are a lot of materials based on Daz Iray Ubershader on sale. Same as was with 3DL - many materials packs and only a few really different shaders.
what is more advanced is tricky question. Iray is more physicall correct. It was made such, it was made for archviz and product renders. It allows measured materials and measured lights and so on. All this is aviable even in DS al long as you can work with Shader Mixer. Suprefly is Cycles-based, and Cycles is animation render at base level. So basicly you can't make precise diamond ring render, but have less troubles making believable skin.