Hi Liverpoolgirl,
My 20 year old son and his mates stayed in Kavos last June and they had a ball. THe previous year they stayed in Magaluf and also had a great time. The nightlife was brill in both places. Do take plenty of mozzie repellant to Kavos though as my son was bitten badly (although he was wearing repellant) and had an infection when he returned which required antibiotics.
On a positive side there was plenty to do both day and night and he didn't get much time for sleeping. They're off to Playa de Las Americas in Teneriffe this year. For a fortnight this time instead of the usual week.
Have fun!