Been all over the US, Europe, and parts of Canada and Mexico. There are so many great cities out there, and all are great for different reasons!!! Since no city combines EVERYTHING, here's my favorites:
Favorite Nightlife: New York City (nothing comes close)
Favorite for Outdoor Activities: Los Angeles (my home town) - I've snow-skiied and gone to the beach in the same day (really). Enough said.
Favorite Culture: Rome - Incredible history and Italians are great people
Most Beautiful: San Francisco - it's so scenic it makes me ill
Best Transportation (airport, subway, roads): Munich or Paris
Most beautiful people: Miami - a model everytime you turn around in South Beach
My overall favorite: Los Angeles. People like it or don't, but I love it! Good climate in winter AND summer, the air is the cleanest it's been in ages, and tons of stuff to do. But I still love travelling!!!!