New York is incredible, the fact you know so much of it from TV and films, being there has an added edge to it. I absolutely loved it, just walking around and finding random corners of it with their own vibes. The people are great. The only issue is that you have to walk too far to find a pub, there's not one every 10metres like in London.
Tokyo is fascinating. So much going on, an awesome night out and interesting people. Rio is amazing for the beaches, and scenery though I didn't find it as "carnival" as everyone says it is. For a football mad country there weren't many playing on Copa Cabana, there'd be more on a beach in England if the weather was ever as good!
If I had to pick one in Europe it would be Nice. Not huge, but it's got a casino, a cool old town, Monaco nearby and mountains and beaches.
Shanghai for the view of the skyscrapers... stunning. But beyond that there's not a huge amount.
Overall, Hong Kong (have I name dropped enough places?!). Excellent food. Beautiful scenery. Awesome markets, cool buildings and beaches. For me any city that offers all the shops/restaurants/bars and also has an opportunity within close range to get out and unwind is truly special. Hong Kong does that. Sydney is close, but Hong Kong has more going on for me.