I voted for the 2000's mainly because we know so much more about producing a good sounding speaker today than we have ever known before. Because of this a good sounding system can be put together for a very reasonable amount of money.
I got my start when my dad bought us a system in 1969 or so. I consisted of a turntable, a Dynaco SCA-35 tube integrated amp and a pair of AR 4x speakers. I was amazed at the sound that little system produced and was hooked. In high school I put together a pretty decent little system consisting, in the end, of a Hafler DH-101 pre-amp, Dynaco FM-5 tuner, a fancy Sony PSX-500 turntable, a decent 3-head cassette deck, an SAE 125 watt per channel amp and a pair of Dynaco A-35 speakers. That system blew away the usual dorm room system of those days: a Pioneer SX-424, a Technics turntable and a pair of Smaller Advents.
In reality there were several golden ages though. In the 1970's it was the golden age of power and pre amps. It was possible to buy an amp with lots of power and power reserves to drive low impedance loads at basically any price point. This was a good thing. On the pre amp side, phono pre amps with incredibly low noise and great RIAA correction became common, even at low price points.
In the 80's the emergence of the CD as the playback medium of choice was a real highlight. Some of the early transfers were pretty bad and sounded almost as if the mastering engineer had just left the RIAA preemphasis curve in place. But others sounded fantastic, listen to Dire Straits "Brothers In Arms" for a look at what digital sound could do. I got on the digital bandwagon pretty early, around '84 or so, and engineers pretty quickly learned how to exploit it to make really great sounding recordings.
But the 2000's and on really take the cake. Those nice sounding Dynaco speakers I bought on sale for $150/pr in 1975? More than $700 in today's dollars. Those AR 4x's from 1969? Over $800 today. You can get a pretty badass pair of bookshelves for that much today that will sound way better than those old AR's ever did. Since, IMHO, speakers rule your system and the current era is the era consistently high quality speaker design, this is the golden age.