The Mother of All Canon Lenses (TMOACL). The color, contrast and sheer image quality make this the best Canon lens in my opinion.
I rented this lens for a week long trip to eastern Oregon. It doesn’t have the reach of the 500mm or the 600mm, yet it is lighter with an an f/2.8 aperture.
It takes the Canon 1.4x and 2x extenders with little image degradation. It’s very easy to handhold, and focus on my 5D Mark III was fast and accurate.
I miss this lens already. It does have a few shortcomings though. It’s large and expensive.
I don’t have a have a practical reason to own this lens since I don’t shoot enough wildlife, sports or other fast action pursuits. I will rent it again though when the need arises.