Go for Copenhagen! It's quite cold in April for boating in the Oslo fjord, and it's nothing spectacular. Sure, it's different from most US cities, but Oslo is expensive and there's so much more to see in Copenhagen. (By the way, Oslo can't compete with my home town - Arendal. 4 hour drive from Oslo, and boating here beats Oslo any day. (The city centre is in the right uppermost corner, this is from an island where they throw a yearly music festival, called Hove Festival))
