I've had both. The AT&T DVR is far superior to Comcast and makes rebooting worth it. I only have to reboot maybe once every 4-6 months, not "every other day". A couple times a year I would have to reboot the Comcast modem, too. The internet is really flaky as well. You may not notice it doing normal web browsing, but try doing something that depends on the reliability, like VPN, video conferencing, Live Meeting, etc. Comcast would break the connection several times a day. With AT&T, I've never had the connection break, even after several days of being connected. Just try going to the Windows cmd prompt and run something like "ping google.com" and you'll see how bad Comcast can be.
Maybe it's where you are located. I have VPN on all day without interruption when I work at home. My google ping was 32ms, yahoo was 35ms.
Comcast has 20mb/sec service now too.