Slashdot, because even if they've leaned towards pop science "I'm-such-a-nerd" bullshite in recent years, at least they still have actual conversations about technology.
Even Redditors never seem to believe me when I tell them that the site was basically like Slashdot or Hacker News in its early years. To them Reddit has always been about epic funny pictures and "If I get 200 upvotes I'll adopt a cat!"