After trying the original Canon 50mm F1.8 II, and the new 50mm F1.8 STM, I swapped it for an older used 50mm F1.4 and couldn't be happier.
It's sharper than the two mentioned lenses at all the faster apertures ( wider than F2.8 ).
Here is a quick test shot (with my old 1D mark II) right after getting this lens.... wide open @ F1.4. Canon EF 50mm F1.4 USM by mistaspeedy, on Flickr