I have my roots on prime lenses, with time on becomes too used to zooms, I did. Recently I was looking at what are the best prime lenses for the Canon 6D, by best I was looking at resolving power. My normal zooms could resolve between 11MP to 14MP out of 20MP that the camera has. Surprisingly, the first two lenses in the DXO list came from the new Sigma Art lenses. The Sigma 35mm f/1.4 Art could resolve 18MP on a 6D, I believe the fourth lens was the Canon 35mm f/2 IS USM. This lens also resolves 18MP on the 6d but it is not a f1.4 lens.
I went to my photo store and checked both. I was willing to pay the $900 for the Sigma but after carefully comparing bokeh which is important for me I found this to be much better with the Canon.
After I bought the Canon 35 f/2 IS USM and shooting anywhere between f/2 and f/5.6 I found my images with a detail I've never seen before from this camera. Is like I've upgraded the camera from 13MP to a camera of 18MP, quite a difference. Colors are very contrasty too. IS is awesome.
What to say, I just sold my normal zoom L lens.