Based on my knowledge and research, the best and free online AI art generator is Craiyon. It is a web-based tool that allows users to create art images using a free version of the AI image generator. Craiyon uses advanced machine learning algorithms and deep learning networks, such as OpenAI's DALLE 2 and Stable Diffusion, to generate high-quality images from text prompts. The output of the AI art generator is impressive, with the ability to create detailed and realistic images that resemble pop art, marble sculptures, clay ceramics, or watercolor paintings. Additionally, Craiyon offers customization options, allowing users to fine-tune their creations to fit their desired style. Overall, Craiyon is an excellent choice for those looking for a free and powerful AI art generator that can produce stunning works of art.