hello whiter, in my experience,
Sweden's transportation is fast and pleasant whether it may be a train, bus or ferry.
Malmo has international train connections and you can travel from Malmo to
Stockholm in 4 hours. You can get on the high-speed X2000 train and it will reach stockholm 4½ hours. But regular trains can take up to 6 hours. so I recommend X2000, not only for its fastness but also it's convenient. You can call them on 0771-757575 and enquire about where to get the trains, cost of the ticket etc., and as well as book your ticket. Hope this helps!