While there is no clear-cut answer to this question, and the purpose of these FAQs is not to endorse products, multiple threads have been created on this topic that should provide some information into what most BBR users would recommend as the "best" modem for Comcast.
NOTE: These opinions are NOT endorsed by Comcast in any way, shape or form. All opinions are respective of the poster.
*This FAQ is based on user knowledge from a volunteer core of BroadbandReports' members. This FAQ in no way constitutes official information from Comcast or any of its affiliates.