The process of decaffeinating creates imbalances of taste and sometimes flattens out the flavor of the beans. When buying decaf we strictly avoid any bulk or ground coffees and purchase directly from a local roaster.
We had a decaf coffee the other day from that local roaster. It was an otherwise excellent Indonesian single-origin coffee. It was rich and full but it had an unpleasant sourness that we don't usually associate with that region. When we mentioned this the roaster gave us a good tip on choosing decaf coffee. It all has to do with those coffee regions we've been talking about. Each of those regions - Africa, Latin America, and Indonesia/Pacific - have their own unique taste characteristics.
These flavor profiles are each affected in different ways by the decaffeinating process and if you are buying single-origin decaf coffees you may notice heavy swings, like the sourness in the otherwise rich Indonesian.
So, our roaster friend said, when buying decaf look for blends instead of single origins. Look for blends that have a mix of beans from two or three regions - that way their complementary strengths can smooth out and mask deficiencies from the decaffeinating.