I'd say Rebel Rhyder too. Sometimes I wonder if those two huge black dicks at DAP even feel their fucked up ass. It seemed to me that it is already boring for her and she doesn't even know that she has dicks in her ass.
I'd say Brittany Bardot has the biggest prolapse, but honorable mention for Monika Fox. The biggest asshole would have to go to Lady Ana - nobody else routinely takes male double anal fisting, and pretty rough too. Although Rebel and Adeline run her close...