So, let me throw my $.02 into the ring here.
First of all, I am a huge fan of some music from every decade since the 1920s. That does not mean I think every decade was created equal, however.
I think the first misconception we have to put away is that corporate involvement either kills or saves music. This is clearly not true. Sometimes (eg, the 70s) mainstream music is the real deal, the stuff that will last for generations to come, the stuff people will be listening to far into the future. Sometimes (50s, some of the 00s) the mainstream stuff is pap that no one will remember five minutes from now that has no true artistic merit. That is why there has always been some good music, since the 20s. You just have to know where to find it.
With that preface, here is what I think about the decades since the 60s. These are off-of-my-head impressions. It may be that if I actually went and checked charts for these decades I'd remember tons of things good and bad that I've forgotten. But I'm a musical optimist. There's always more good stuff around the corner, if your know where to look...Also, this is talking more about popular music that feels connected to its time, not to timeless or world music thatm ay have been created then but shouldn't really count for or against the decade. I'll throw in some great live performances for fun and because they really give you a taste for the time:
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1960s - Genesis. The beginning. The big bang. This is when modern pop music was revolutionized ever by the Beatles and was giving all of its grounding and form. Everything that came after is based on this decade. However, not everything here (Despite the claims fo aging hippies and young hippie-wannabees) is worth the effort. Not everyone that played at Woodstock was a visionary. Not everyone that took drugs and picked up a guitar will be remembered forever. However, there were some truly transcendent and special things going on in this decade, eg Jimi Hendrix, Santana, The Beatles, The Rolling Stones, The Who, Bob Dylan, Janis Joplin, Beach Boys, Kinks, etc. etc.
Best Live Performance: Santana playing Soul Sacrifice at Woodstock:
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1970s - This was the apex of mainstream music. There was simply no better time in history to own a radio. The hippies had grown up a bit, the record engineering was better, and some entirely new genres took off. For me there are too many great bands from the 70s to count. For example, just in 1971, the world first heard monumental albums by: Led Zeppelin, The Who (at their prime), The Rolling Stones (ditto), David Bowie, Marvin Gaye, Jethro Tull, Yes, The Allman Brothers Band (Duane Allman is the messiah), Funkadelic, Mahavishnu Orchestra, John Lennon (his solo work), Rory Gallagher, America, Can, ELO....This is a decade stuffed full of excellent, excellent music. And I didn't even mention Fleetwood Mac, CCR, Queen, Elton John, Deep Purple, Simon & Garfunkle, Aerosmith, etc etc
Best live performance: The Allman Brothers Band playing Statesboro Blues at the Fillmore. No video unfortunately, but the best slide guitar of all time.
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1980s - Mainstream music takes kind of a nosedive but it's okay because we get punk and the beginning of the underground scene. This is when the really really good punk, post-punk, and new wave stuff started coming out. If you were turned into the mainstream all you'd get was michael jackson and synthesizers (though there is some arena rock that is actually great music, eg Queen, Bruce Springsteen). But if you had an ear to the ground, you would have heard some of the greatest artists ever, such as The Cure, The Smiths, Black Flag, Sonic Youth, The Clash, Sex Pistols, Pixies, Dead Kennedys, The Pogues, Bruce Springsteen, Violent Femmes, the Pogues, Queen, Minutemen, and Queen. And this is not to mention the huge heavy metal explosion with the likes of metallica, iron maiden, and a zillion other awesome bands if you're into that type of thing. [BTW - I am not anti-synthesizer in particular; I'm anti-synthesizer when it's used for BS like disco (which existed in the otherwise sublime 70s, btw) but some electronic music really is fantastic].
Best live performance: Queen at Live Aid. On many people's lists, this is the greatest live performance of all time. Freddie Mercury is transcendent and the crowd of zillions is in the palm of his hand.
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1990s - Watershed decade. The mainstream radio stuff actually wasn't bad at all compared to the eighties, but the indie music renaissance was truly getting going and some of its first stars remain its brightest. Some really bad record engineering practices really took off in this decade but that's a discussion for a different time. Some of my all-time favorite albums are from the 90s. Artists include Nirvana, Neutral Milk Hotel, Guns 'n' Roses, Sigur Ros, Oasis, GY!BE, Massive Attack, Jeff Buckley, Cocteau Twins, My Bloody Valentine, REM, Radiohead, Smashing Pumpkins, Rage Against the Machine, SOAD, Weezer, Soundgarden, and that one song from harvey danger.
Best live performance: Nirvana unplugged in New York playing The Man Who Sold The World. Not much moving and it's played to total silence, but it's so freaking beautiful...
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2000s - Radio music takes a decided nosedive, mostly due to the influence of hip-hop (the 00s musically only really seemed to start at like 2004 anyway). But oh boy the underground music just kept coming. This is when I got really into piracy so I remember a lot of the play-by-play album releases especially after '06. Daft Punk! Explosions in the Sky! more Radiohead! The White Stripes! The Decemberists! Saltillo! Of Montreal! Battles! Death Cab! QotSA! Wilco! Lady Ga Ga (kappa)!
Best live performance: Can it be that an electronic band actually performs well live? I'm not sure what to choose for this decade. But I've never heard a crowd go more insane than the one here.
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2010s - I am at this point thoroughly removed from whatever might be considered mainstream at this point. Almost every time I hear something mainstream it either sound like some nasally imposter trying to be as good as real indie bands or some myrmidon grunting to a beat. (Though occasionally the good stuff makes it big -- Ed Sheeran is good; Fun. is good.) I feel at this point that it may actually be too easy for just anyone to distribute music and it becomes harder to find good stuff not because of corporate BS but because you have to find the people who are generally talented as opposed to the people who just fit some sort of mold. However, in that talented group, you have Real Estate, Bastille, Janelle Monae, Beach House (their album Bloom may be my favorite of the past five years), Bon Iver, Fucked Up, Of Montreal, Vampire Weekend, M83, etc...
Best live performance: Janelle Monae playing "Come Alive" at Glastonbury, probably. It's for the ages. Amazing.
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It's hard for me to say what the best decade is, though if I were forced to pick it might be the 70s. My point here is more - there's always good music. Just gotta know where to look.