Much like wine, matcha is sold in a very wide range of quality levels (and a very wide range of price points to match). This quality is determined by where it is grown, how it is cultivated, when it is harvested, and how it is processed. Grade designation and pricing is entirely up to the brand selling the matcha.
As far as health benefits, matcha is one of the most concentrated sources of antioxidants on the planet. These compounds help fend off free radicals, the molecules that nutritionists believe are responsible for accelerated aging, tissue damage, and inflammatory issues. One antioxidant found in matcha, EGCG, has been shown to help support metabolism and aid in weight loss.