I like Dublin, although never spent more than 2 days at a time there.
Loved Amsterdam, stayed well away from coffee shops and red light district, apart from to visit the Museum of Our Lord in the Attic, which was brilliantly done. I'd love to go back, we stayed in a stunning hotel, found public transport great, and enjoyed the food.
I like NYC but the first time I went thought it was nothing like I expected. Still think that now, but I like it anyway.
I lived in Melbourne for years and absolutely adored it. I think in lots of ways it is a locals' city though, I can imagine tourists being a bit bemused, depending on what they're interested in. I think the pp who derided it as a second rate city is perhaps meaning that in terms of as a tourist? It consistently ranks top, or very highly, in the most liveable city ratings.
I also love Hong Kong, for personal reasons.
I've never particularly regretted visiting anywhere, but wouldn't rush back to Madrid, Bilbao, Basel or Glasgow. I might be unfairly maligning Glasgow but the weather was shite both times I've been and that does kind of colour your impression of a place. The other 3 I enjoyed visiting but feel that I've seen what I would want to see in those places, and have no reason to go back.