In my travels, I always try to utilize public transport. Been to quite a few world cities, and riding CDMX's subway was a rather unpleasant experience. The trains are BEYOND packed. (Even outside of rush hour). Carriages aren't necessarily air-conditioned, so there's the element of sweaty bodies pressed against each other. It sort of felt as if CDMX subway system could barely keep up with the crush of incessant crowds.
Pros - fare is cheap, 5 pesos ($.30). Trains cover fair amount of territory. And, Transit Police present on train platforms.
Cons - hot, stuffy subway cars, escalators don't work in every station, and, elevators are hard to find.