Like someone else said, a lot of funny and popular memes like Trollface, Yo Dawg, Rage comics, Bad Luck Brian, and Scumbag Steve originated in 4chan, and that is their main source of popularity. However, it's quite improbable to come across anything noticeably funny by visiting the site directly, since 4chan has over 700,000 posts daily (according to knowyourmeme), and most of them are garbage. A friend told me that I'll find good retro games discussion and porn there (especially porn), but I returned disappointed in that regard as well. Overall, their contribution towards making the internet a funnier place, is immense. However, I'd prefer finding their funny stuff from a secondary source, rather than browse through hundreds of un-funny jokes/memes and people insulting each other in the site, hoping to find something great. Also, the site doesn't load properly on my mobile, and that certainly doesn't help things.