if i'm chosing between this lens (Sony 85mm f/1.8) and the Samyang/Rokinon f/1.4, which one should I choose if I'm looking for performance and image quality?

I can't tell which is sharper at f/1.8. Sony f/1.8 has more smooth bokeh than Samyang/Rokinon f/1.4 (see https://enthusiastphotoblog... ) at f/1.8. Overall I think Sony f/1.8 has better image quality.

The Samyang/Rokinon has sharper corners at 1.8. If you measured in a lab, you’d probably find the Samyang/Rokinon sharper across the frame, but both are tack sharp in the center to the point where differences are irrelevant at 42mp.
But lenstip.com just tested the Samyang/Rokinon and actually found near record breaking sharpness, better than even the GM. (My copy definitely was sharp but not as sharp as theirs).