Like you, I'm a Comcast customer who wanted to stop renting the hardware. I went with the NETGEAR Nighthawk AC1900. Although I generally agree with the concept of "separates" I purchased the combo modem+router unit and have been very pleased with the performance. It is Comcast approved, supports very high speed on the Comcast side (24x8 channel bonding) and the most current protocols on the home side (802.11 AC). WiFi coverage now extends into the back yard, so I've removed the WiFi repeater I'd setup some years back.

Although separates (one modem, one router) are more flexible if you change ISPs, that's not happening anytime soon. Having one unit reduces troubleshooting and wiring. There are cheaper options than the Nighthawk, but I'll still save money before two years of rental charges are up, and I'll have a slick piece of hardware to show for it.