has better bokehwith ugly CA btw Sigma's bokeh is nothing compare to Russian Helios M40-2 analogue. If you prefer excellent bokeh - buy Russian stuff.
Sorry, I don't care for the bokeh of the M40-2. It's unique for sure, and I've seen it put to good use in some shots. But it's very distracting and 'nervous' for most shots. I much prefer the smooth, diffused backgrounds of the Sigma.
Needless to say the M40-2 is a specialty lens (manual focus / stopped down metering / adapter required). On top of that, it's the wrong focal length for this discussion, it's not nearly as sharp wide open, and it does not have nearly the contrast as any of the 50mm lenses being discussed. Again, it has a unique look and that can be put to good use at times, but it's not a substitute for the lenses being discussed.
As for CA: the Sigma is worse than the Canon f/1.4, but much better than the f/1.2L. At any rate CA is pretty much a non issue on digital where it's easily corrected. And with the typical subject matter for these lenses you often won't even need correction. In fact, now that I think about it, I don't think I've used CA correction on more than 1 or 2 shots from my Sigma.