Several years ago I film tested the canon 70-200mm F4L, 80-200mm vario sonnar, 100-300mm vario sonnar and the 100-300mm F5.6L canon.
The 70-200mm F4L was good, but the 80-200mm vario sonnar had vastly superior flare control, had better edge sharpness. The 70-200mm F4L was better at F4 and F5.6, but from F8-F16 the vario sonnar was demonstrably superior. And the 80-200 vario sonnar had much better performance in the middle to closeup distance performance. If you value landscape performance and flare control the 80-200mm sonnar is the lens for you.
Now the canon 100-300mm F5.6L is an older, discontinued, EOS lens. Its construction is a little plasticky. But the image quality is first rate, bar none. It is sharper, center to edge at any focal length and aperture compared to the 100-300mm vario sonnar. And it is one of the few eos lenses I have ever shot that actually has flare control comparable to a contax lens. It also focuses ridiculously close at 300mm and has superb closeup performance. It is a real tragedy that canon never redid this lens with USM motor and better construction. The image quality of the 100-300mm F5.6L is a revelation. Please, canon, resurrect this lens.
My tests of these lenses were with film on EOS bodies, I can't imagine that the same wouldn't be found when shot on a digital sensor.