To replace a Comcast Gateway (Modem and router combo) first you need to go to the Comcast web site and look at the modems that are compatible with Comcast. You can get a Gateway or a separate modem and router. I prefer a separate modem and router. Makes changes and debugging issues easier. I have Comcast and got a Motorola Modem for a service higher than I have so I would have future expansion as my previous modem reached 'end of life' and was no longer supported and Comcast did raise my Blast service. So I recommend a modem that is faster than your speed tier that is approved by Comcast. Then I got an Archer C8 for my router. It has served me well over the past few years. In selecting a router you need to look for the features you need. Do not go super cheap. I recommend you get an “AC” model with gigabyte ports (check LAN/WAN speeds 10/100/1000) as they will support both old and newer devices at the best speeds. If you have special requirements such a long distances for WIFI, need “port forwarding”, need parental controls, need to attach a printer or disk drive, or such, look at the router model reviews specs. If you get a mid or higher range model you can grow into you will be happier. I currently have a MB8600 modem with a TP-Link Archer C8 router with over 20 wireless clients, 4 wired clients including Ooma phone system and a security DVR, and a USB disk drive for several years and it is not near its limits. I have Comcast 200 speed tier and I get speeds over 200 most times. Without knowing all of your needs and such, I can not recommend a specific modem and router. I recommend you buy new hardware and from a place that accepts returns in case you have an issue especially for the modem.