Trip to scandanavia reccomendatiopns.?

Me and my friend are 22 and are flying from philadelphia to Stockholm this June.. We would also like to visit either Copenhagen or Helsinki while we our there and I was wondering which city would be our best bet. Also how much spending money would we need not counting the air fair.. We plan to stay for 10 days and stay cheap/ hostels etc.... would we get by with $1,000 usd.... Any other recommendations are welcome