Copenhagen or Croatia for a weekend in May?

Hello, the best airline ticket prices for May from my European home city are to Copenhagen and Zagreb so I can't decide on which of the two would be better? I haven't been to Scandinavia or the Western Balkans yet so each trip would be a first for me and I really have no preference. I feel that perhaps Copenhagen would be warmer and sunnier in summer while May seems like a better time for Croatia than summer as the weather would be slightly warmer.

I wonder if Copenhagen would be still cool around May 23-25? The thing with Croatia is that if I end up going there I will probably take the bus or train to the coast and stay there, for example in Rijeka as the closest coastal city to Zagreb. If I decide on Copenhagen I will just stay in the city (or maybe incorporate a quick visit to Malmo one of the days). It takes around 2,15 hrs by bus from Zagreb to Rijeka and 4 hours by train.

It won't be a museum- or sight-heavy visit, I just want to experience a few days in a different country, experiencing shopping at local supermarkets, tasting local food and just looking at the Adriatic/Baltic sea, strolling around promenades or the canals of Copenhagen. I live in a landlocked city so Zagreb would feel like more of the same but if I get bored with Rijeka I could go back there earlier before my evening flight home to explore it as well. Thanks for any advise!