I snapped this a few months ago at Plaza Meave on Eje Central, in the Centro Histórico. They’ve got the biggest spit (trompo in Spanish) that I’ve seen in the city. It’s always crowded, and fun to just sit and watch — the taquero works like a madman, slicing meat with one hand and catching it in a tortilla.
The tacos are decent. I’ve only had them at mid-day, when the meat isn’t quite caramelized enough. If you want to go, it’s located on Eje Central, north of Mesones.