re: Best modem/router for Fiber

You're going to get stuck with whatever ATT gives you. I still have an NVG589 which probably went out of support five years ago. It's fine, set it in passthrough, it becomes a bridge that functionally does nothing that concerns your network. A bridge technically converts one medium to another (fiber to Ethernet, or Coax to Ethernet, etc.) If it's in passthrough mode, it doesn't do DHCP, DNS, or anything else that is cool. Your router then controls it (which is what you want.) You can set DNS at the router to force Cloudflare or other encrypted DNS, etc.

Get an AX router. I have TPLink now, but will switch to Synology soon. I have 5200 sq feet, and one router reaches everywhere I need.