Angela - wouldn't say Poros was really lively. But there are some 'hot' spots on both Kos and Crete which would keep a 14 year old occupied.

Kefalonia is my favorite but I suppose it's what you are looking for for your daughter and yourselves, Corfu is very touistry with plenty to do for the younger eliment, Zanti, maybe Kos all depends on if it is a Greek Island you want if not Spain has manly lively resorts which are also at times very English, but this is for you enjoy your holiday because that's what holiday are for to enjoy
pojo

We stayed in Kos Town when our daughter was 15 (10 years ago) and she still says what a fab time she had.

Plenty to see and do on Crete for a family.