Recomendations for Croatian R & R

Hi all, my little brother is flying out from the States to meet me in Slovenia in a month's time... As I can only take a week's vacation off work, that is all the time that we will have to take a little trip down to the beautiful Croatian coastline... My question for you, is where should I take my brother, considering there are so many awesome places but only so little time... Looking for somewhere with great beaches, fairly solid nightlife and if possible, a hostel (so that we can meet other travelers).... Been to Dubrovnik, so I think we can pretty much scratch that... But there are many islands I've never been on, I know Pag is a party place, any other recommendations? Korcula, Hvar, Rab? Thanks in advance!