personally, I would not take one without the other – either way.
Even with the best of certifications, experience is of extreme importance. That will be the case whether we will have industry standards or not. What a certification ensures, though, is that the person stays up to date on his knowledge through required CeCs, has a valid CPR/AED and has liability insurance. That is the reason why the club at which I teach requires that the trainers hold a nationally recognized certification even when they have a college degree in an exercise related field.
I cannot give you a ranking as you asked for. On the other hand, I do not believe that personal training is viewed as an ‘amenity’. To me an amenity is towel service and a hot tub.