I started with zoom but prefer prime. It depends of the project I am shooting. (event, sports, arts, wildlife, landscape, portrait, packshot)
But at end of day, when it require quality, I use prime...
Best prime I love to use, 85 1,2L, 100 Macro 2,8 IS L, 300 mm 2,8 IS L II.
Zoom I am using quiet a lot, 17-40 4 L, 24-70 2,8L, and 70-200 2,8 IS L II but do ot have lot of fun with it
This is difference, I love to use prime, and it s ok with zoom.
Mounted on 5D3 and 1dx.