the Canon 50 1.4 looks like a good lens too, but I've read that the particular USM motor used in it is ancient & prone to breaking down. The 1.2L has the full time manual adjust high end USM motor, but because it's such a heavy lens focuses slightly slower than the 1.4. The sigma also seems to have more vignetting & chromatic aberration compared to the L from the reviews I have read.
I broadly agree with the post but there are fact which are quoted wrong and need correction. The 1.4 also has full time manual focus and the reason why the 1.2L focuses slowly is because it is focuses by moving the lens elements in the front unlike the lens design for other USM lenses - not because it is heavy.
5D3, 6D, 600D, RX100
16-35L, 24-70L II, 70-200L II, 100-400L, 50L, 85L II, 135L, 24TSE, 40, 100 macro, 18-55 II, 55-250 II, 600RT x 4
I come here to learn something new, not to learn how bad my gear is - I know that already ;-)!