Router configuration with ISP FTTH modem/router

[slh]

So you have 500Mbps-1Gbps fiber and need a router READ THIS FIRST

It's such a frequently asked question over the last few years that we really need a post we can point people to. So your cable company rolled out 500Mbps or 1Gbps download speeds, or you have 1Gbps symmetric fiber (GPON/EPON) from ATT or Centurylink or Orange or whoever. You realize your old all in one router from 2009 is not up to the task of handling this, but hey by now stuff should be cheap and available that will handle your new fiber connection right? So you want advice about a router for…