i used both before, and i personally would recommend the Canon. its cheaper, lighter and has good enough image quality.

Not to say the sigma is a bad lens, but the design is kinda dated and it is a lot bigger/ heaver with slightly faster aperture only. also being older sigmas, there are chances that you will be fighting with back/front focusing and it is super frustrating.

i owned the 50mm f1.4, it is basically unusable at f1.4 if you shoot anything far (around infinity focus), the image is way too soft and it makes you think if it even focused at the first place. but the image quality is acceptable if you shoot mostly portraits (anything from half body length to close up).

build quality wise it is quite plasticky, basically any older canon lens (non L ones) have really cheap build, so the 50mm STM is actually better.