火车或者飞机都是不错的选择，看你的时间安排,火车座位宽敞，有FREE WIFI

我们这次去了4个城市， 另加Gothenburg(Second largest city of Sweden)
Copenhagen to Stockholm(Flight) 1 hour($65), Stockholm to Gothenburg(Train) 3.5 hours ($38)
Gothenburg to Oslo(Bus)  3.5 hours($28)   OSLO  to Copenhagen(Flight) 1 hour ($48)

Download App OMIO you can book both flight or train
Download App VY you can book train or bus, also you can book the train/bus from airport to downtown