I am a total Top, and my favorite position to fuck a bottom is to put his legs on my shoulders, and really grind on him. A similar position would be grabbing his ankles and bending him way back so he's doubled up, then piledrive him by straddling his hips and sitting on his butt while I fuck him. Started doing that with a college buddy of mine, I liked it, and he loved it. It became our position, and even when I wasn't fucking him in that position, I was still sitting on him! Loads of fun!