RedGIFs

RedGIFs is the backbone of the adult-GIF world. After Gfycat exited NSFW, RedGIFs became the default host for short adult clips, which is why you see it embedded all over Reddit and other communities. On its own site you get a fast, endless-scroll feed with strong tag-based search, so finding a specific niche is quick, and it is free with no account needed to browse. Everything is user-uploaded and moderation varies, and by design it is short looping clips rather than full-length video — this is for quick, scrollable content, not a movie night. As the central hub that essentially all adult GIFs pass through, though, it is the obvious number one in the category.