I've been using 4chan for longer than Reddit and Lemmy combined. Mostly /vg/ (games), /g/ (tech) and /a/ (anime, manga).
Mostly for discussion. /g/ and /vg/ are decent for asking stuff if there's a general about the topic that you want to ask info about, you want a relatively fast answer, and it isn't something overly asked (e.g. "which distro should I use?" "INSTALL GENTOO" tier). Just make sure to not trust anything said there.
Other boards are typically too slow (like /ck/) or cesspools (like /b/, /b corta/ /v/, /pol/).