First of all the taste of coffee like any other drinks is a bit a personal choice. Although there are definitely bad fermented coffees around, one can say that the average Yunnan coffee quality is considered by coffee experts as reasonable. The quality of the coffee is to a high extend depending how it has been processed after harvesting and how it is made as drink. Arabica is the best variety to drink, but there are >100 varieties. Robusta is more used for Instant Coffee. Mixtures are made to bring the price down, since Arabica is a lot more expensive than Robusta. Advise go around and sample.