Le Cellier has a lot of hype and a few steaks on the menu, so if you are on the DDP it is included. People want to eat there and maximize value of the DDP.
They also have cheese soup and pretzel bread that people rave about.
San Angel is busy, but I have always been always been able to go and eat there without an ADR.
I think the longest I ever waited for a walk up was 30 minutes and that was during spring break.
It also has great atmosphere even if the tables are way too close together.