I have the HCO sliders; that's my black LR3 in his pictures. They have been quite tough for everything that I've done. As others have noted, one real difference between the HCO sliders and the RS ones is the additional coverage that the RS ones provide in the compressor area.
I haven't seen the RS sliders in person, but I suspect they sit lower on the vehicle than the HCO sliders in order to cover the compressor in the stock position. I think if you combine the HCO sliders with the HCO compressor bracket to move the compressor up higher you end up with more ground clearance in that area. This is just a guess since I haven't seen the RS skids, if someone knows either way for sure please post.
Also, if you combine the HCO sliders with their skids, in the end you get more coverage than the RS sliders alone - HCO has some really stout tcase and gas tank skids. We've actually jacked the LR3 up on the tcase skid. Of course you can add the Rasta skids to the RS sliders, but I prefer the HCO skids to the Rasta ones.
Here are some pics of the HCO gas tank and tcase skids to see how they work with the sliders. If people want more/different pics let me know.
http://grendel.smugmug.com/gallery/6013404_bqJNP#376008378_9GiNc