I started with the 35L followed by the 35 Art and I bought a 50 Art on top of it.
First I couldn't choose and decided to keep them both as they are both perfect primes.
As I had to do a wedding I sold 35 Art for a Tamron 24-70 2.8 VC (almost as sharp as the 24-70 2.8LII)
With the Sigma 50 Art, the bokeh is a lot better and the lens is also killer sharp in comparison with 50 1.2L.
This summer I plan fashionshoots, 50 1.4 Art is ideal for halfbody shots of the model & the clothes in the picture.
35mm was too much environmental, models want more close shots, they don't like environmental portraits.
So 50-85-135 (or 70-200 2.8) are ideal for modelshoots.
For commercial shoots, example a doctor in front of his practice,... the 35mm is wider.
Sometimes I doubt to re-sell my 24-70 2.8VC as I don't plan too much weddings in future, but but I will keep doing events, so it's more handy than a 35 Art.
Another small difference : when i'm in a restaurant I can take a pic with 35L of my wife + daughter while sitting over them.
With my 50 Art I have to stand up and take the pic from further.
So short : both lenses are perfect, but for halfbody portraits/fashion the Sigma 50 Art is the way to go.