Antigua Guatemala is the antidote to Guatemala City. Unless you really need to, don’t even think of staying in the capital! The drive to/from the airport is hardly any longer from Antigua than from the capital and taxis/buses ply the route if you don’t have your own transport. If you want to visit the capital it is 45 minutes away. Antigua has become a major centre for Spanish Language Schools and receives a lot of tourists, mainly from the US but on the whole is not overwhelmed by them. Its location, overlooked by a volcano, is superb and its relatively small size means that it is easily accessible on foot. Its climate is pleasant, its hotels and restaurants cater for every taste and budget.
The town doesn’t contain any buildings of “world class”, but its inscription as a WHS reflects the totality of its colonial heritage and the atmosphere it generates - the nearest comparison on the American continent I can identify would be Ouro Preto in Brazil. (This review was related to a visit in summer 1985)