Energy Star has a lot going for it mainly because it is really the only internationally used energy use standard. The idea is to make it available for the top 25% performing products in a category, with the baseline updated every few years for improvements in technology - so, a five star product today is better than a five star product three years ago.
Not sure if Panasonic in NZ use the Energy Star stickers in store, but several Panasonic TV's are advertised in NZ as being Energy Star - 5 star. IMHO it is better than a rough guide.
It is also an open standard, so results can be verified.