If I were you, I’d avoid Downtown at all costs. It has its fans, but between the windowless rooms, the noise and the improvised air conditioning, I’d just go elsewhere. I’ve stayed there twice and vowed to never go back.
The HR can feel special if you get a nice room on a high floor facing the park. It’s proximity to museums is a great plus and it has one of the best health clubs of any hotel I know in CDMX. It’s not the most luxurious and the service can be spotty, but it has a striking modernist design, great art in public areas and a good location.
Enjoy your trip, Mexico City is a very special place.