If I understand correctly you want a big city recommended. Do you want a city where a car is not necessary? Then I say New York city, possibly Chicago. Does climate matter? If you want beach weather you can consider cities in FL, but you will need a car, and the cities are set up differently than NY. It is more like extremely crowded suburbs in my opinion, because the residential tends to be somewhat separate from business. There are many places around America that have a reasonable sized downtown area, but don’t come close to being a city like NY. I think I need more details to know what you are looking for. Which European cities would fit the bill? Then we can come up with something comparable maybe.