My favourite cities are those that you can walk around if you want to and have good public transport if you don’t. New York City falls into that category. I spent quite a bit of time walking around NYC sometimes going from the top of Central Park to Brooklyn. It’s the best way to see a city and meet people.
Other big cities I’ve liked walking around include: Tokyo, Paris, Hanoi, Buenos Aires, Rome, Amsterdam, Berlin, and others I’ve forgotten about.
For the US trip, after the first two weeks of hiking with a group, I ended up going to cities that are perfect for walking around: San Francisco, LA, Austen, Chicago, Boston and NYC. A few times, people at the hostels I stayed at told me not to go to certain areas — during the day or night (or both) because it was dangerous. For example, in Chicago, I got talking to a volunteer at the hostel at breakfast. The conversation went from a typical traveller chat (Where have you been? Where are you going? etc) to him giving me lots of tips about what to see in Chicago, where to go and where to avoid.