It depends on what you plan to do in the evenings/nights. If you're the type to go out and walk around, go to a restaurant or listen to live music, then skip the zocalo immediate area. Roma would be more relaxful or even a hotel near Bella Artes which is lively at night. I've stayed at the Gran Hotel, Hampton Inn, Zocalo Central and a few smaller hotels right at the zocalo and it was the same thing every time. Everything practically shuts down early. The only reason to stay at the zocalo is because of a festival, event etc at the zocalo in my opinion.