HN has outlasted Slashdot by a wide margin at this point.
IIRC, Slashdot stopped being great around the same time as the decline of the Digg era. It started to sink in quality around 2007, which gave it ten years at most of being a central part of the online tech community (1997 - 2007).
I started reading HN in 2008. It's lasted nearly twenty years as an incredible community.
Here are some graphs: