I will echo the suggestions for Motorola/Arris modems. I've used them for over a decade and they have been rock solid. The SB6141 is perfectly fine for all but the extreme speed tiers, but for $20 more I'd consider the SB6181 modem for some future-proofing. Comcast will continue to let you bring your own SB6141, but has placed it on the end-of-life list for leasing.

I have also had some bad experiences with combo devices in the past and have a longstanding preference for a separate modem and router. But I acknowledge that there are reliable combo devices out there if a single box is your thing. My top choice in standalone routers these days is Asus, especially the RT-AC68U.