honestly, the fan art landscape has shifted a lot. Back when the anime was airing, Tumblr was the undisputed king for creative, weird, and super in-character art. Artists there really captured Saiki's deadpan exhaustion and the sheer chaotic energy of his friends. Nowadays, I'd say Twitter (or X, whatever) is where the most immediate and viral art pops up, especially for ship dynamics like Saiki and Teruhashi.
For pure, concentrated volume and quality, Pixiv is still the heavyweight champion. Japanese artists dominate there, and the technical skill is often breathtaking. You'll find incredible scenes reimagined in stunning detail. But if you're looking for more humorous, meme-inflected, or crossover art, Reddit communities like r/PSIkiKusuo can surprise you with hidden gems shared by dedicated fans.