Here, the third one, the best roller - the Rumble Roller.
I don't use this on my back. I am too "thin" and it presses into my ribs if I use it. Also, I don't want anything pressing on my spine for safety reasons. My boyfriend is thicker than I am and does use the Rumble Roller on his back.
This is AWESOME For legs though. The plain roller and Y roller barely feel like anything on my legs. But the knobby parts on the Rumble Roller are wonderful at pressing into my legs in various places and kneading the muscles. So this is definitely the one I want to use on my leg muscles.