I have tried several different routers and firmwares.

The #1 thing that made accessing the Internet faster was implementing domain level blocking of the top ad and tracking servers at the router level (e.g. doubleclick.net)

OpenDNS/Cisco let's you set this up domain level blocking in about 10 minutes that also covers iOS devices, if you don't want to tinker with openWRT.

Previously OpenDNS would monetize by "hijacking" mistyped domains, but they switched to a friendlier free consumer/paid enterprise model.