I own sigma 30 f1.4 for canon set up. It is almost identitical to Canon 35 f1.4 wide open except the different focal length.
It is smaller in size and lighter in weight. Sharp in the centre and MTF falls off quickly reaching the corners. The bokeh is beautiful and it is very capable in all sorts of lighting.
Though sigma 30 f1.4 tends to blow out highlights in harsh lighting, the problem is solved if you shoot raw.
There is a lot of complaints about this lens not being sharp enough etc. In real life, it is a all round lens - a lens I brought along to a Thailand watermarket where the boat proved one old chinese saying - a boat can either carry people or sink them to the bottom of the river. This lens has been all used to the extent I cannot re sell anymore. A good lens.
Examples of 31 f1.4
f1.8
f1.6
f1.8
f2.0
Fa 31 is a great lens especially for protraits. IMHO, it is better than sigma when it comes to elliciting "atmosphere" feel.