Dall-E 2 and then Imagen took the cake with AI art tools, but they were closed APIs. Things were actually good enough to be generally interesting. Before this, img2img / txt2img / etc weren't very interesting.
Stable Diffusion is the first open source tool, and it doesn't require a zillion GB of RAM. so anyone can download it to their computer, and it's getting hacked on and improved on at a faster rate. IIRC there's a good version of the model down to 4 GiB and it runs on M1 CPUs now, making it accessible to an actually pretty large group of people.