Honestly, I would regard Bulimia as the worst, as it can lead to Anorexia. The person regurgitating anything eaten, making the mind think it has eaten, and start to use up energy, to digest the food, which, has just been regurgitated.
But, Anorexia and Bulimia are serious mental illnesses, which affect judgement, and emotion. People with these illnesses shouldn't be ignored.
Both deceases are horrible for the human body. There really is no worse one. If you have either you the illnesses, you have to get help. Thats pretty much all there is to it.
But for the sake of the discussion, Bulimia poses more health threatening symptoms on a human. Bulimia could lead to other diseases, instead of Anorexia, would is pretty much just malnutrition as the biggie.
Although both are almost equal, i would have to say bulimia is worse. When the person gags themselves, the stomach acid burns the esophogus lining, which can cause major damage to the body.