The prime is a lot brighter and creamier Out of focus rendering as a result. But it's harder to use, exact focus is critical and composition is harder work and slower. The zoom has far more versatility, it's wider and a lot longer in it's focal range. It's beautifully sharp, as sharp a prime. It's quicker to use due to the zooms versatility, it's got a quicker AF system too. A pair of primes and matching cameras is required to cover a simular focal range...but still lacks the versatility. I tend to use three cameras for my wedding work: a 35mm f1.4, 85mm f1.2 and a 16-35IIL for wider stuff. But, a single 24-70L is far easier to work with in brighter weddings.