I think it's only fair to do it by body-fat percentage lost.
During my initial efforts to lose weight....I biked, swam, played racquetball and worked-out like a demon all while eating about 1,500 calories per day. Over the course of one month, I GAINED 2.5 pounds, but lost nearly 3% body-fat. It's really about losing fat.....
People who cut carbs quickly lose/drop glycogen supply. Each gram of glycogen requires 3 grams of water...this is why obese people are said to initially lose "water weight"...they aren't losing real fat. Seriously, the body can only breakdown/metabolize true nasty fat at a certain rate: surely you don't think these people can lose 17 pounds in just one week????? Well, not 17 pounds of fat. And let's not forget about all the lean muscle the body will dump too! As soon as they start eating anything more then low-calories, the body re-establishes the glycogen and up goes their weight.
Nahh....it's gotta be about body-fat. Get some calipers and let those competitive chubs battle it out over the pinch!