Re: Which has been the best decade for music?
My favourite decade is the 70s. The "best" in terms of influential is the 60s (whether one likes the music and bands from that era or not, they exercised more influence on subsequent music than any other decade in the 20th century). All of this applies to pop/rock in the broad sense of the term.
If we're talking jazz, then I'd say the late 40s to mid-60s were, indisputably the "best" and my favourite. Coltrane, Davis, Brubeck, Baker, Adderley...(I could go on and on and on and...)
If we're talking classical (in the broad sense, not the technical sense), then I'd say late 17th century to early 20th century (I'm a big enough fan to appreciate music from across that span, but not knowledgeable enough to reduce it to a specific decade or two). As for favourites, I'm most partial to mid-to-late 19th and 20th century Russian composers (Tchaikovsky, Rimsky-Korsakov, Prokofiev and Shostakovich, among others) and early 20th century English composers (Vaughn Williams, Elgar and Bax, among others), though I enjoy music from a wide variety of composers.