Popularity is one measure, but this is misleading, since most things that are popular are actually a good enough quality but not the best. Take anything, clothes, wine or cars. The most popular product is never the one that is the best quality, it is the one that has a stronger price to brand performance perhaps.
There are also many standards in coffee the two most common as far as quality of the raw bean grading is concerned are the African standard which is to list coffee as Grade 2 (since Grade 1 is not allowed to be exported), and AAA, AA or AB. Unless the coffees have been externally graded this actually means very little.
Grade AA means that in a crop that was the biggest size, and size is not always a good measure for quality even if there is an actress and a Bishop involved. In fact the smallest grade Pea berry normally is a better grade than the AAA grade.
There are however three trustworthy ways to judge a coffee before it is brewed:
The cup of excellence or COE, which is a competition that is run once a year, then the winning coffees can have boasting rights, this however only includes the South American coffee growers at the moment, so it discounts the largest growing area of Equatorial Africa (and home of coffee), there is some inclusion now by African countries are not listed a full members yet.
Micro lot auctioned coffee, 1000 this stuff is very scarce in South Africa, and the coffees are cupped each week, micro lot coffee represents a portion of a growers produced that is represented as the best week of a harvest. Micro lot coffee is always listed as such. The most important is that you judge it yourself. We have a thing that we use called the drink-ability index.
Once we have finished tasting a coffee we see how fast we consume the rest of a sample, if the sample is drunk quickly then it has a high drink-ability index, if we find that the next days we still have some left then it has a low drink-ability index. Why not try it yourself. You do need to be a big consumer though, we drink between 5 and 20 cups a day depending on the drink-ability of the coffee.