Transportation options from Copenhagen to Stockholm...

Same question posted in Swedish section.

Train or plane are the best options, both have pros and cons.
The train goes city centre to city centre and you can sit and relax the whole way. If you can catch a direct train, it's 5 hours 20 minutes. If you travel early morning or late evening it can be very cheap. Look at www.sj.se

Plane is faster, but you have to deal with the hassle of getting to and from the airports to the city centres and the whole airport security, checking in, finding your gate etc. From city centre to city centre the whole journey is about 4 hours. Tickets are usually cheap, but remember that you also have to pay for train or metro from the airports to the city. The Arlanda Express train in Stockholm is a bit pricey.

Overall the train is a bit slower but more relaxing.

I'm weighing in based upon what my husband and I did in May. We traveled by high speed train from Copenhagen to Stockholm. I purchased tickets in advance on the Swedish train website thereby saving money. As soon as availability I purchased our tickets in February. The upside I saved money but the downside was the ticket was non refundable, a choice I made to save even more, but I traveled using the best case scenario mentality. It was a great trip and I would do it again. Traveling by train is more comfortable and was less of a hassle to us. My final decision to go with the train was definitely based upon what I read on this forum. Roomier seats, ease of walking up the aisles, ability to bring food on board, and arrival in the city center where we stayed in our Stockholm [Airbnb][1 Airbnb made for great transitions from one city to another.
I had no problem using my American credit card & had advised my bank of my plans in advance. I did have issues booking Norwegian trains but had to use a different browser (Firefox) & I found PayPal worked for all train, ferry reservations in Norway. (I booked our own Norway in a Nutshell journey on my own not using the main site that handles the bookings for a fee. There were others who did the same that day.)
Sonja

Thank you Sonja. We've decided to fly from Berlin to Copenhagen and take the train from Copenhagen to Stockholm. Thanks for sharing your experience. - Kevin