There's some other GPU engines out there that are as good as well, but most rely on CUDA, the same as Octane.  The problem is also, they are either very expensive, or geared only to the high-end platforms (Maya, 3dsmax).  There's standalone versions, but no plugins for Poser or DazStudio, for any of these.  They are all faster than Luxrender/Reality, with results as good as Octane.

Furryball is a really good one.  It's as fast as Octane, using the Nvidia CUDA, but also has some deeper features that are usually only seen in CPU rendering.

Arion - This one uses ALL availabe resources for rendering.  All CPU's and CUDA GPU's at it's disposal.  That makes it blazingly fast, and capable of things no GPU-only render engine could do.

Again, those engines are only plugin-ready for Maya or Max.  I think Arion can plug into some other platforms, but they're all very expensive as well.

I think the best GPU engine that doesn't cost anything right now is CYCLES, inside of Blender.  You can use that one for free, and it's very good.  Not sure it supports SSS or some other things yet, but the light quality is on par with Octane at least.  IDL in Poser is good, and can produce great results, but it take a lot of setting up to get there, and by the time you figure out how to get good results in your scene, you could have quickly transferred the scene over to Blender and just re-applied the textures there manually.  Plus, there's some major flaws in the Poser IDL still.  Light leaks, spots in tight corners of enclosed spaces, and diffuse reflectance issues that are impossible to fix except in post.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.