The key differences between the Canon 17-55mm and 24-70mm lenses are their focal lengths and maximum apertures. The 17-55mm lens is more suitable for wide-angle shots and has a wider maximum aperture, making it better for low-light conditions and creating a shallow depth of field. The 24-70mm lens offers a longer focal length range and is more versatile for various types of Photography, such as portraits and landscapes. The choice between the two lenses depends on your specific photography needs, with the 17-55mm being better for wide-angle and low-light situations, and the 24-70mm being more versatile for different types of photography.