None of them. I wouldn't want to give up the conveniences of modern technology for anything the 20th century had to offer, even if the current culture wars make me sick.
The 80s would probably be my choice if I were forced kicking and screaming, but that's probably just childhood nostalgia talking before I was too young to notice real problems in the world.
The 90s? Overrated. Too many squandered opportunities and mistakes from world leaders which just laid the foundation for today's problems. The initial Internet bubble just masked underlying problems under a false veneer of prosperity.
As for the rest, forget it.
1900s? Still culturally in the abominable 19th Century. Teddy Roosevelt is the decade's only saving grace.
1910s? WWI. 'Nuff said.
1920s? Better than most, assuming you live in the Anglosphere or even France. You don't want to live in Russia, or China, or Germany, or just about anywhere else though. And things do not end well at all. It's also 100 years ago at this point, and I wouldn't want to go that far back.
1930? Worst decade without a World War. The Depression, the rise of fascism, Stalin running the Soviet Union into the ground, Japan rampaging through a civil war torn China; who the hell in their right mind would want to live in this decade?
1940s? WWII. 'Nuff said.
1950s? Decent amount of postwar prosperity, but American culture is dominated by stodgy buttheads. Okay, I'm white, straight, male, and not a liberal, so I'd probably fare better than others, but I don't have a rosy eyed nostalgic view of the 50s. And it's still 70 years back, so everything is woefully outdated for me. America the only place you want to be, because everyone else is rebuilding from WWII, decolonizing, or behind the Iron Curtain. Well, there's Canada too I guess. Maybe Australia and New Zealand as well.
1960s? Gag. Rising social unrest, Vietnam, hippies, and other various problems combined with a culture that mostly sucked. And then by the end, all the pstwar prosperity is over.
1970s? Even worse than the 60s. Stagflation and other economic problems galore, Watetgate and its aftermath, the energy crises, a total lack of style from EVERYONE (the 80's doesn't get a free pass on style at ALL though, WTF was that decade thinking!?) disco and so on. I had the misfortune of being born in this horrid armpit of a decade.
So yeah, the 20th century was probably still on of the best centuries since H. sapiens "evolved*", but I wouldn't want to return to it, at least not blind. Gray's Sports Almanac style cheating is the only way I'd want to do it, though I'd likely go stocks instead (sell in 1987 and then again in 1999!) Or have fun rampaging in New York's real estate market at the time where I can enjoy the sublime pleasure of stomping on people like Donald Trump and Leona Helmsley. But I'm the kind of guy you would not want to give a time machine to, because I would deliberately start screwing with the timeline everywhere.
Note that some of this is very much tongue in cheek.
*"Evolved" in the sense one should expect from a very cynical misanthrope who notes with disdain and contempt how much human behavior is not at all far removed from the rest of the apes.