There are two distinct questions here. The decade that objectively produced the best [Popular/Rock] music would be the 1960s, obviously. Though, since it's all arbitrary anyway, I think 1065-1975 would be the best answer. But if the question is "What is the best decade for music," then the answer is overwhelmingly the 1970s for so many different reasons. ETA: I'll even go an extra step further and say that the most "important" decade for music was the 1930s.