I've own the Canon 50/1.4, Sigma 50/1.4, OM 55/1.2, Rokkor PG 58/1.2, Zeiss ZE 50/2 MP, OM 50/1.8 and probably a few others that I can't remember.
First, most full frame digital sensors cannot accept light that impinges from a cone outside the f/1.6 region, so it's moot whether a fast lens is of any particular benefit. Still, I expect this will change over the next year or three as new sensor technologies are adopted. As an aside, some CSC sensors accept light from far wider angles and CAN exploit f/1.2 optics. I have tested this on my Fuji X-E1.
So based on this, the lens with the best sharpness / bokeh trade-off is a converted Rokkor 58/1.2. It can have difficulty reaching infinity focus but this can be dealt with using live view. I've not observed spherochromatism either. Typically $600+ for one in good condition - quite amazing for a 40 year old lens....
The Zeiss ZE 50/2 MP is superb at all apertures, exhibits negligible focus shift on stopping down and is about as sharp as can be had. It can also do 1:2 macro which is sometimes helpful.
The Sigma 50/1.4 has excellent bokeh but suffers from spherochromatism and considerable focus shift. This is fine provided you don't stop it down - but then it becomes a one-trick-pony.
The Canon 50/1.4 is very good. It does have vignetting when wide open (typical of fast lenses) but its biggest drawback was slow autofocus and fragility. It is a very good lens and excellent value for money.
The OM 55/1.2 is soft when wide open and sharp at f/2. I'm not finished with it yet. typically $550+
The OM 50/1.8 is sharp at all apertures but has weird bokeh - probably a result of its rudimentary aperture control. That said, they can be had for about $30 and are compact, well made and robust.