I think Mexico is generally no less safe right now, with the current exception for the city of Oaxaca (the rest of the state should be pretty normal,) and the disruptions in traffic and services caused by the PRD civil disobedience largely confined to Mexico City.

With lower fares from MIA, Mexico City is always a good bet - and ZIH is an easy shot with lots of flights. With ~88,000 people and a history, it is IMO much nicer than some of the more recent highly-developed areaslike Ixtapa, the area north of Puerto Vallarta (particularly the newly-named Litibú, which is the next area targeted for instense development by the Department of Tourism.)

Colonial Taxco has been preserved by laws that require all construction conform to certain restrictions and is a nice place to visit (even in summer, it is at a high enough altitude to be spring-like and the rains are generally brief showers in the afternoon and occasional night rains.) Nearby is the interesting but undervisited archaeological site of Xochicalco (place of flowers,) a Toltec citadel where several cultures met periodically to adjust their calendar using a kind of observatory, and the extensive and interesting caves "Grutas de Cacahuamilpa."

Acapulco is old enough to have some history - but new enough it was only a small fishing village in my lifetime. (My uncle Ricardo used to fly down to ACA in his light airplane - he was offered some land, but he figured the palce would never amount to anything. Ooops!) So, no colonial buildings, but definitely some aging infrastructure, so rather than stately age, it suffers from seediness in some aspects IMO.

Cancún was selected and designed in the same process - but some of the coastal towns a couple of hours south of Cancún are nice (not so much surfing, due to the barrier reef that extends up the Caribbean coasts of Belize and much of the Yucatán peninsula,) and Mérida on the weekend is a great place as well.