Well, we use ours maybe half the time or less, depending on the exact piece. The Wedge, I feel, is the most convenient and can be used by just about anyone to get your hips at an optimum angle. The Bon-Bon is not only great for double penetration (try that with a pillow!) but really great to get the "ass straight up in the air" position that I really love. We use the Ramp slightly less often, but find it very comfortable and a great way to get into some crazy positions as well as straightening out the body for a good massage. We also love our Escape as well (not sold on Eden) as a very comfortable play space that we can move around (we have wood floors and they hurt!).
The thing about Liberators verses pillows is that the pillows have a tendency to slip around, while the Liberators are made to kind of "stick" in place because of their material. Liberators are also easy to clean and don't wear out easily.