My 50 1.4 was a complete dog. Complete mush at anything below f2.8. I bought the Sigma on a whim with the intention of buying the 50 1.2 later. Later never arrived.
The Sigma 50 1.4 is very sharp and has good bokeh. It is usually good to focus, but occasionally stops before achieving complete focus. The focus action is a bit harsh compared to Canon lenses.