Thanks for starting this thread; the recommendations are really helpful. Does Sonic need to enable anything on their side to allow me to switch from AT&T-supplied modem/router to my own modem? I have an Actiontec GT701D but its built-in settings (which include a Sonic preset) don't seem to work.
I'm currently rocking the Zhone 6729 with dual lines (X2). It supports ADSL2+ Annex M as well as VDSL2 17a (bonded) and 30a (single line only). Unfortunately it is not made anymore I did stockpile a bunch and have like 4 spares ready to go should my current one die. They still pop up on ebay from time to time. I especially like it because it supports VLANs and you can get creative and bridge the DSL connection to one VLAN while keeping the modem also bridged in, allowing you to throw DMZ devices into that VLAN for direct access (if you have the static IPs) while using the modem as a gateway for everything else.
B0 Traffic Type: PTM
B0 Line Rate - Upstream (Kbps): 55491
B0 Line Rate - Downstream (Kbps): 127280
Line 1 is up and in sync at 19397kbps up and 60728kbps down.
Line 2 is up and in sync at 36094kbps up and 66552kbps down.
DSL of all flavors is a dying dead-end technology so there aren't going to be many manufacturers putting effort into new devices.