Crete
Crete is probably the best known island in Greece because of its variety and many tourists. The island has a lot of history and also have great beaches and night-life that should satisfie you. However, Crete is a big island and that's probably where the 'variety' comes in. When I went there for some years ago we ended up in the most shitty place and could hardly even take a shower without fearing company (cockroaches need to shower too?), and the weather really wasn't that great. However, we travelled a lot during that time and Crete turned out to be so much more than what I could even imagine. Besides, people are extremely friendly there; at least that's the impression I got. Beaches are wonderful especially around Shania, so be aware where you book your hotel if you decide to visit this island. Overall, don't get stuck in one place because this island has many great places to offer!