I chose the Extra Firm Rumble Roller and it is like a foam roller with treads on it, they are not foam in any sense and the treads are hard. When I first started using it, all I could do was lay on it in some areas, such as my poor hip flexors. No rolling was taking place, the pain was too much to bear. Soon I became used to it, the muscles started to relax and I was rolling like a champ! I did find that I had small bruises all over my hips after my first few intense rolling sessions though.
I encourage you to get a roller, and if you are a tough cookie, and tend to have tight muscles, go for the Rumble Roller, you will be glad you did!