Which is better as a summer holiday: Croatia/Greece?

Which country do you suggest would be better for a group of 4-5 friends on a relatively low budget? We are thinking of going for about 6-7 nights in August. Within Croatia, I was thinking Split or Dubrovnik, since I know they have loads of activities and night clubs, but I've never been to Greece so I know less about it. And if you suggest Greece, which part of it do you suggest we go to?