I use Black Diamond Telekneesis knee pads and they work great for me. They are a bit on the pricey side, but I like the fact that they also protect some of your shin below the knees and are low profile. In addition, the straps used to fasten the pads to your legs are designed well and are super comfortable.
I've tried both Skeletools and Azzpads and I prefer Azzpads since they are lower profile while providing similar protection for the tailbone. I took out all the extra padding from the Skeletools shorts with exception to the pad covering the ass and they are still pretty bulky. Out of the 2, if you're looking for "cushier" padding that protects more than just your tailbone, skeletools is the way to go as long as you wear fairly baggy pants. If you're looking for no-nonsense tailbone coverage, Azzpads are for you.