For me, it's /pol/ because of the news, polandball, and just the idiocracy. /s4s/ is also pretty cool for the endless shitposting.
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I don't frequent 4chan very much anymore, but I use to lurk /b/ like it was nobodies business. Too many summerfigs now-a-days. I feel like a few years ago the population there was more diverse, and now it seems like a bunch of liberal wips that just found out they can see naked pictures online. I bet you could find multiple threads on the board right now that should go in /s/. Maybe it's just nostalgia.