I am hoping to go to Denmark this Spring, any suggestions that are NOT Copenhagen?
Also I was informed by a friend that she had issues with transactions while she was there and had to use her other cards as Barclaycard (perhaps it was a mastercard?) was not accepted in a lot of places. Has anyone found this to be true?
More places accept Visa than Mastercard in Denmark.
Also annoying: merchants there often charge fees for foreign-issued credit cards. See https://www.travelcodex.com/why-denmark-more-expensive-than-planned/
In terms of where to go, other than Copenhagen, try Bornholm. It is an island in the Baltic, and is part of the Danish state. The best way to get there is by ferry from Copenhagen. The island itself is quiet, with a few towns, and great biking opportunities.
The last time I was in Denmark I didn't have the Barclaycard yet, but I haven't had a problem anywhere else in Europe. It is possible that your friend's issue was with the chip and pin. Barclaycard is not a true chip and pin. It does work at automated pay stations, which is a big plus over all the other US cards, but at all other places it is a chip and sign, like other US cards. That may have been your friends issue if she was expecting chip and pin.
Anyway, enjoy Denmark!