I've heard from a number of sources that the sigma 35's bokeh is blah.. and not as impressive as the Canon option.I don't see anything wrong with the bokeh on the sigma 35I find the bokeh in the Sigma 85mm not as pleasing as the same, shot with my Canon 85mm f1.2L II. Performance wise, the Sigma smokes the Canon 85 but that is not the subject here.
The good news for bokeh is that the 50 is basically a modified 35, so it should be a slightly better longer focal length version of that lens (very slightly sharper on average, less distortion, same bokeh in other words).
I actually went the opposite way with the 85mm Sigma though, the bokeh of the Sigma has a nice pop to it, with beautiful interesting OOF highlights, the Canon's is very very flat, which can be a good thing if that's what you like, but I liked the Sigma 85's better.
here is an example @ 1.4