Well I just spent my first day learning on the slopes last wednesday, wearing the Demon DS-1450 Low Hard Tail Impact Shorts pictured above. They do a decent job of covering and protecting you, but for someone like me who weighs over 200 pounds, I think its going to take either the azzpads or skeletools to provide enough impact protection. I ended up busting my tailbone when I fell hard early in the day, and kept hitting it the rest of the day since I was learning. They were better than nothing, and I will continue to wear them. But I think people over 190-200 pounds should invest in thicker padded shorts if they want to protect their tailbone.
I can't comment on the RED or Dianese impact gear, as I have'nt used them. But my Demon shorts are decent, and well made, and I would recommend them to someone lighter than me in heartbeat.
Just my .02