For the moment, I only saw Stockholm last August, and the closest geographically located city I visited is Hamburg.
Stockholm surprised me, both in positive and negative.
In the positive: fantastic nature, anywhere with public transport you are never more than 20 minutes from a forest, subway itself is a great tourist attraction with its architecture and its artwork.
The level of the shops is very high (unfortunately also prices, especially for food, books and sportswear, on the contrary the best city in Europe to buy discs, surprisingly cheaper than in London, Paris or Berlin and with great assortment).
Great museums, places like Skansen and the cemetery in the woods (Skogskyrkogården) have been models for similar places in other countries.
In the negative: except for the subway, Gamla Stan and the elegant Vasastan, both Norrmalm and peripheral neighborhoods are surprisingly anonymous from the architectural point of view.
Also I did not expect so many shopping malls, and so few single-family houses.
In Hamburg there are many more single-family houses and they are much more beautiful, large and stylish, it is a much more residential city than Stockholm.
Another big difference between the two cities is public transport, as Hamburg is far more extensive than Stockholm, but they are almost the same as subway Kms and Hamburg completely eliminated trams in 1978 (Stockholm reduced them in 1967), so the subway network is inadequate and travel times higher than Stockholm. And there are many more graffiti and tags in Hamburg than in Stockholm.
The Hamburg cemetery (Ohlsdorf) is the largest in Europe and deserves UNESCO's recognition at least as much as Stockholm's Skogskyrkogården.
I hope to visit Helsinki next year, especially for the presence of two national parks near the city and Euro as a national currency, Copenhagen is more expensive, Oslo even more than Copenhagen and Bergen is too rainy.