The Guatemalan capital, Guatemala City is a center of indsutry and commerce. There aren't much attractions for tourists but visiting the museums and exploring the local markets aren't such a bad idea.
It is a very different city in comparison to Guatemala City. It's quiet and filled with spectacular colonial buildings with lots of international flavor as well. This is the place where great majority of travelers choose to base themselves in Guatemala.
The countryside around Antigua and Guatemala City is a spectacular landscape of volcanoes, forests of pines, meadows, corn fields and coffee plantations with occasional villages. It is well-worth a visit. Looming over the capital is the Pacaya volcano which is one of the most active volcanoes throughout Central and South Americas.
Most well beaten path travelers opt to head straight to Antigua, mistakenly thinking that Guatemala City is entirely some sort of hell hole.
If you are arriving by air, you will be coming in from Aurora International Airport. Since 2005, it's under-construction for its remodeling project which was about time since the airport looked very outdated in comparison to other Central American countries. To move on from the airport, you can either take scheduled shuttle buses to Antigua or taxis from outside of the terminal.
Guate City buses cost 1 Quetzal as of early 2007 and they offer a good way of getting around if you aren't heading through outlying slums.
Since Guatemala's governamental system is centralized in Guatemala City, many national and international non-governamental organizations are based on the capital city as well. There are numerous foreign NGOs in Antigua also since Antigua is a hub of foreign volunteers. See those articles for information on volunteer opportunties.
Given the opportunity, most Guatemalans would opt for something besides the usual corn and beans with some occasional meat of some sort. Don't expect great cuisine there, but the food can be quite good.
Guatemala City has rather alarming rate of crime in some areas. Stay out of trouble by using plenty of common sense. In Zone 1, after dark, walk directly to places you want to go and know where you are going. In the Zona Viva (Zone 10), follow normal precautions anytime, including after dark. Don't get drunk in any of the nightclubs and then stagger back to your hotel. THAT could attract a would be robber there.