So, thank you so much for your answers and very instructive discussion. I didn´t expected to induce sucha a technical debate.
I ordered the Canon 85mm 1.8 and I will give it a try. Even if I am a bit sceptical about the CA´s.
The Bokeh of the sigma looks nice, but since it is a bit of an investment and I already have the sigma 17 50 2.8 I would like to try another focal length.