In my opinion, the stove or air popped popcorn is better than the microvave ready popcorn. I find it tastier not overly seasoned. Yes, it is easier to popped in a microvave but there is danger as reported from a study of the FDA.

Reports from the FDA that the bags used in microwaveable popcorn when heated breaks down into a substance called perfluorooctanoic (PFOA), it is identified as a "likely carcinogen". The Environmental Protection Agency also has found an acid which when extracted from the chemical causes cancer in animals, and may cause cancer in humans too.

The chemical diacetyl (found in fake butter flavoring) , which is FDA approved, posed a danger too when inhaled for extended period such as the disease of popcorn factory workers, called "popcorn workers lung" (medically known as bronchiolitis obliterans). But it needs further studies so they can avoid the risks according to National Institute for Occupational Safety and Health.

It is also easy to cook popcorn so forget the Microwaveable ones, it is better for your health and avoid worrying about it.

According to my source, the coating on the inside of the bags can break down under the heat of the microwave and into a possible carcinogen, perfluorooctanoic acid. The amount of the acid from one bag is approximately one fourth of the estimated daily intake, so whether or not you eat any won't matter that much. The site also says the butter flavor can be a hazard to your health, specifically your lungs.