For two millennia, medicinal mushrooms have been mainstream in Asia. Now, America is taking notice and interest is rapidly "mushrooming." With the sprouting of this new industry follows issues of ethical quality claims between competing brands.
All medicinal mushroom species are plagued by this. Most fiercely debated is red reishi (Ganoderma lucidum), the most popular of all medicinal mushrooms. So this article will primarily focus on that species, but it's generally applicable to all species of medicinal mushrooms.
An obvious caution is to stay away from cheap, mass-produced reishi. It may be merely dried and pulverized. In order to be medicinal, the mushroom cell-wall has to be broken down. Mass-produced reishi may be mostly inert and ineffective.
Then there are the real therapeutic grade red reishi brands, which are produced with much more care. But even here there are big differences between brands. Each claims to be the best, of course, because they want to sell their product. So lets set the facts straight and be independently informed consumers.
Following are the three primary ways of creating reishi extracts. Each method yields different medicinal compounds, all of which are shown in scientific studies to have important properties.
1. Hot Water Extraction (polysaccharides, etc.)
2. Alcohol Extraction (triterpenoids, etc.)
3. Fermentation (arabinoxylanes, etc.)
The water soluble compounds, primarily polysaccharides, are powerful anti-tumor agents, immune enhancers and strong antioxidants. 
The alcohol soluble compounds are mainly triterpenoids, a large group of related compounds. Scientific studies suggest they help stabilize cholesterol, blood pressure and clotting. Most importantly, they are the anti-inflammatory compounds so critical to many of reishi's suggested uses, including arthritis, allergies and asthma. 
And then there are the new and unique medicinal compounds that get created when reishi is fermented. These "secondary metabolites" have their own therapeutic properties, different from the first two groups, including anti-tumor, immune support and blood-sugar balance. 
Since this article is not intended to elevate any one brand over another, no brand names will be mentioned. Nevertheless, the author does know of two highly reputed brands (American and Japanese) that claim only hot water extracted red reishi is of any value and that alcohol extracts are useless.
Of course they do that to promote their own brand. In reality both hot water extract and alcohol extract contain unique medicinal compounds that are all very important.
To determine if a brand of reishi (or Ganoderma) contains all the important medicinal compounds from the mushroom, find out if it utilizes both alcohol and hot water extraction. An additional plus would be if it also includes fermented reishi.
As a last point, when you look for the best reishi extract, one thing to look at is the form it comes in. For example, any reishi extract that fully dissolves in a water-based liquid such as coffee probably only contains hot water extracted reishi. So while reishi/ganoderma coffee certainly makes for a superbly delicious and healthy cup loaded with polysaccharides, it won't include the important anti-inflammatory triterpenoids.
Alcohol tinctures, on the other hand, are well worth considering because they may be a blend of water and alcohol extracts. The way to tell is if the tincture is cloudy. When water-soluble polysaccharides get mixed with alcohol, they fall out of solution. Cloudiness in an alcohol tincture indicates high polysaccharide content. Just shake before taking. Tablets and capsules can contain hot water extract, alcohol extract or both. You need to find out from the manufacturer.
 Boh B, Berovic M, Zhang J, Zhi-Bin L, 2007. "Ganoderma lucidum and its pharmaceutically active compounds." Biotechnology Annu Rev 13:265-301.
 Tang YJ, Zhang W, Zhong JJ. "Performance analyses of a pH-shift and DOT-shift integrated fed-batch fermentation process for the production of ganoderic acid and Ganoderma polysaccharides by medicinal mushroom Ganoderma lucidum." Bioresource Technology 2009 Mar;100(5):1852-9.