I use Growstones brand media, and it's excellent. It's very light weight, and holds a ton of water. My plants love it, roots grow thick, fat, and juicy. It's a rather expensive media, and is a bit of a pain to clean old roots out of because they have so much surface area. I've also used washed lava rock with excellent results, for about half the price. Lava rock has the additional bonus of silica, which is abundant in soil, and something most hydroponic plants are missing, unless supplemented. Growstones compared to hydroton - environmental issues and cost aside, from just a performance perspective.... Growstones will allow you to wait longer between feeding intervals than hydroton. Both are excellent, but growstones will hold more moisture for longer than hydroton. If you get a hot day, or there's a problem with your system, growstones offer a nice backup of nutrients that your plants can survive off of for longer than just hydroton. If you ask my cats, they prefer hydroton, because it rolls nicely. It makes the ultimate cat toy. They are much less excited about Growstones.
I just picked up a bag of growstones today. Came here to see peoples opinions. Seems like good stuff. Glad i bought it. Will update this thread later with my opinion of the stuff!