It's been forever since I was there, but Taxco was a beautiful, well-preserved colonial era silver mining town. I don't know how much if any mining still goes on in the area, but there should still be plenty of silver shops that cater to tourists. Read the State Department bulletins on their website about the security situation in Mexico - there were several mass graves found near Taxco containing several years worth of fallout from the drug wars, which had been previously considered to be largely confined to the border states with the US.
Mexico City is big, noisy and heavily polluted because it is trapped in a high altitude basin that traps the smog. Nonetheless, the Anthropology museum is absolutely a must-see, world-class museum. Plenty of art on display throughout the city - poke around on the New York Times' website travel section for suggestions of galleries and other museums. You will see great luxury alongside poverty to rival some of the worst in the world - I remember places that could compete with Cambodia.