The Four Seasons and the Nikko are two of the best hotels in Mexico City (the latter if you want to grab some decent sushi). Westin is also acceptable and probably half the price, although you can get good corporate rates at the FS sometimes. The very large majority of Mexicans are really friendly and helpful to strangers, but there is crime in the Distrito Federal, so be careful flagging the green cabs in the street. Always try to pick one up from a taxi stand. The city has a lot of wonderful sights though so don't be deterred. The Pyramids, the Anthropological Museum, the Main Square, etc. are all fascinating.