The best, just ....

Expensive, heavy, bulky but extraordinary sharpness, superb optical quality at all focal lengths, efficient autofocus even in dim light, moisture and dust sealing, etc ....
There is no miracle: the so-called equivalent objectives that sell for half or a third of the price do not have the same qualities and fishing by one or other of these criteria.
I personally use this goal for photos "indoor" (concerts, school holidays, ...) and for remote portraits. A treat. A significant investment but I recommend it to fans amateur photographers. If perfection exists in this focal length range, Canon has probably reached.