There is no one best zoom lens for Canon DSLRs, as the best lens for a given photographer will depend on their specific shooting needs and preferences. However, some of the most popular zoom lenses among Canon shooters include the EF 24-70mm f/2.8L II USM Lens, the EF 70-200mm f/2.8L IS II USM Lens, and the EF 100-400mm f/4.5-5.6L IS II USM Lens. Each of these lenses offers a different focal length range and maximum aperture, so it's important to choose based on what you'll be using the lens for most often. In general, wider aperture lenses (like the 24-70mm) are better suited for low light shooting and shallow depth of field effects, while longer focal length lenses (like the 70-200mm and 100-400mm) are better for telephoto applications like sports or wildlife photography. Ultimately, it's up to you to decide which features are most important to you in a zoom lens and select accordingly.