I've visited 5 WHS in Central Mexico in October 2014 and I've really liked Guanajuato. It is different from the nearby cities of San Miguel de Allende and Queretaro, it is much more colourful and its layout is so strange, set against the hills and with so many underground streets!

It gets complicated to get around by car (a GPS here it's really useless, because underground and overground streets overlap and the GPS doesn't know exactly where you are..), so it is better to park somewhere and walk around. The different sites are fairly far from each other, so you may need to drive again to get to La Valenciana (where you can also get down to the mines, other than visiting the church). Spectacular is the view point from "El Pipila". In October it is very crowded because of the festival of Cervantes, but it's nice to see so many stages all around the city. Unfortunately the Theatre was closed during the day of our visit