Many factors determine the quality of a particular product.
Coffee grown in Colombia is reputedly better than, say, coffee grown in Idaho.
On the other hand, Colombia isn't known for it's potato crop. Like many fruit and vegetable products, geographical location has a major impact on their quality. Unfortunately, the biggest problem with herb quality is in the processing after cultivation. Several articles have been written recently about companies that deliberately misinform the consumer about the contents of their herbs. Several products tested contained little or none of the ingredients listed on the labels.