My vote would go to the Canon 50 f/1.2L. I've not tried the 50mm f/1.4, but have had three Sigma 50s. The first two were terrible. The last was very good, but decided to stick with the 50L for the weather sealing and build quality.
Here is a sample at f/2.8:
Here is one at f/1.8:
Cams: Canon 1Dx, 6D, EOS M
Zooms: 17-40mm f/4L, 70-200mm f/4L, 24-70mm f/2.8L II, 70-200mm f/2.8L II; Primes: 22mm f/2, 40mm f/2.8, 50mm f/1.2L, 100mm f/2.8L, 135mm f/2L, 300mm f/2.8L IS II, 600mm f/4L II
Support: Gitzo GT4542LS/GT2830/G2258, RRS BH-55, Wimberley WH-200