I like the tank of gas analogy. I have a purebred now (Shiba Inu) and have had both mutts and other pure breeds before. I love them all, but I have found that although the mutts are not necessarily healthier than the pure breeds (always go to a reputable breeder) I have found them to be generally more 'intelligent'. Most pure breeds are smart for what you breed them for, whereas mutts seem to have craftiness and the ability to reason things out.