Can't pick any single one of them, but Canon needs to upgrade the low end 50mm, 85mm, and 100mm primes same as the 24mm, 28mm, and 35mm primes.
The 70-200mm f/2.8 IS II does such a good job for me, I sold the 85mm f/1.8. The zoom's IQ & IS make me pass on the extra stop, weight, and switching lenses.
I keep the 50mm f/1.4 because it has a two stops advantage on the EF 24-70mm f/2.8 and three on the EF 24-70/105mm f/4 IS.
Actually, the Sigma 50mm f1.4 DG HSM ART is cheap enough, that I'm considering not waiting for Canon to make the upgrade, or buy the Sigma.