The key features that make an AI image generator the best include the ability to produce high-quality and realistic images from text prompts, the ability to modify and enhance existing images, the ability to generate video, and the ease of use. Additionally, the best AI image generators are often open-source, allowing for continued development and improvement by the community. Other important factors to consider when evaluating AI image generators include the level of photorealism, the variety of styles and effects available, and the ability to collaborate and share creations with others. Ultimately, the best AI image generator for a particular user will depend on their specific needs and preferences.