I like canon 1.4 for the way it renders from focus to out of focus and my copy is a tad sharper at center than sigma. Faster autofocus and more consistent autofocus.
I like the Sigma 1.4 because it has far better bokeh in high contrast backgrounds, and has less halo effects in this kind of environment. My copy, the autofocus consistency is just good with the 5Diii.
I think the 50 1.2, you get the best of both and that 1.2 magic. downside is the focus shift at close range is very noticable. I don't own this lens, just get this sense from bloggers.