I have Canon 6D with 24-105mm and 50mm f/1.8 II right now and I mostly use it to take family and landscape photos. I am really happy with 24-105mm and it will be my goto lens. last time when I was in Zoo, I was handicapped by lack of zoom lense and I am planning to add it to my collection.My budget is 2K and I want to get sharpest lens with best image quality. I am leaning towards 100-400 IS II as it was released recently and obviously has newer technology. I can also consider Sigma and Tamron lenses if they have same image quality as Canon lenses. Any input is appreciated.