It is against popular opinion, but I would never buy a cable modem.
Time Warner was one of the few that never charged a modem rental fee, and then they started to. At the time they introduced the fee, I was a subscriber to their high-end Signature Home triple play package. Signature Home subscribers were exempt from modem rental fees, and the BS Sports surcharge and broadcast surcharge below the line fees that were invented as time went by. On the day they became available, I got a 6 tuner DVR, there were no billing codes that allowed Signature Home subscribers to get 6 Tuner DVRs, so I had too break out of that plan, and I was hit with the modem rental fee. Not that it mattered since work pays for my internet, so I just expensed it. And now it’s a moot point since as said above Charter does not charge modem rental fees.
Here's why I would never buy my own modem. When DOCSIS 3 first became available there were 4 channel modems, then 8 channel modems, then 16 channel modems, then 24 channel modems and now 32 channel modems and even DOCSIS 3.1 from some cable operators. As speeds increase, the bonding of more downstream channels is needed. If I wanted to continue to be able to get the maximum performance of the service I am paying for, I would have had to buy three cable modems over the past handful of years, maybe even 4 as 300 or 400 Mbps becomes a reality as we progress into 2018. Currently I have a Ubee MTA gateway capable of 16 x 4 bonding. With this technology changing so rapidly, in makes no sense to me to buy something that I wouldn’t get many years of service out of before I’d have to replace again as technology progresses.
I would never use the router/wap functionality of a cable modem though. I’ve always had Time Warner, and now Charter put the gateway modems into bridge mode. Wireless, NAT, firewall, DHCP all disabled. I always used my own wireless router, and for the past handful of years, I split that up by getting a wired router and wireless access point. Prior to my collection of smart speakers, I never really had a use for wifi. The only thing I used wireless for was for a printer and my MP3 player, everything else I own is hardwired. I utilize some of the more advanced features on my router that aren’t found on cable gateways or entry level consumer routers such as dual WAN failover, site to site VPN tunnels, real remote management and customized access rules.