The sigma 50 1.4 wins it hands down in the 50mm range. The sigma 35 1.4 art is a superb lens, this is the lens to get if budget is not a problem.
I would avoid the Sigma 50mm f/1.4. A high percent of those lenses have major AF issues [youtube.com]
. This is NOT a firmware issue and cannot be corrected with reprogramming by Sigma.