FiOS is going to be the most consistent from building to building. If you have fiber optic all the way to the apartment, then you know it's going to be solid.

Comcast has upgraded some buildings so that the data is fiber optic all the way to the main distribution in the building. So it's like 99% fiber optic. It still uses coax in each apartment, but a majority of that has been upgraded to RG6 which generally doesn't cause any issues.

In some buildings, however, the Comcast has not been upgraded to "mostly fiber" and the internal coax wiring could still have some RG59u, which is absolute garbage. A Comcast installer will 99% of the time rerun any coax that is not RG6 because they won't get good signal strength.

To your original question though, my GF and I both WFH and we have xfinity. We run simultaneous audio and video calls for work (Teams and whatever she uses), I stream music to a smart soeaker and I have over 20 wifi smart devices on the Xfinity router. No issues with either of our calls. When COVID first hit, there were some minor video issues as EVERYONE was instantly WFH, but those issues seem to have been resolved. Note that both of our PCs are hardwired to the routers, which I'd recommend for work calling.