Look at the M column. The closer the value is to 1, the better the protein brand as the actual protein content is closest to the amount claimed.
This is only one way to read this table. There are other factors as well.
Most important is that the M column is only measuring claimed to actual content by serving. However, the serving sizes are different and the claimed protein content is different to start with. So a powder with a higher claimed protein content may still be a better value, even if the measured amount is less if it had a higher protein to weight ratio to start with.
A good example is NOW which measured 70% protein to a claimed 89% for a ratio of .79. On the other hand, the top line ON measured 51% to 56% claimed for a ratio of .91. But that means 49% of what you are paying for when you buy ON is not protein. Even if ON is more accurate, when you pay for that 5lb tub,
~2.5lb is not protein. With the ON, you need 39g of product to get 20g of protein. With NOW, you need 28g of product to get 20g of protein.
Furthermore, this table does not provide cost per gram of measured protein which, IMO, might be a better metric.
And of course, if you value solubility, that is important to factor in as well.
I would say that this table tells you which manufacturers are meeting their claimed values, but if you want to know which one you should buy, you need to factor in more data points than just column M like, solubility, cost per actual gram of protein.
In sum, dudes patting themselves in the back for buying ON should look at the data more carefully. 49% of what you are paying for is filler.