There really aren't too many difference between them and the real deal however if you want to avoid maybe 1 g of added carbohydrate, some sodium, and maybe some gums for foaming and texture properties stick with egg whites or whole eggs
Im not totally sure if it applies to eggs whites. But your body can only absorb half the protein of uncooked eggs. So its probably not a good idea.
Actually this only applies to egg whites and not whole eggs as the yolk of the egg contains biotin, when you take out the yolk that contains the biotin you remove the agents that binds to avidin preventing absorbtion in the digestive tract--not sure about how this would effect egg substitute though