Finally, we went to Mykonos, by Ferry from Santorini, and we spent there two days and a half.
Mykonos was different than Santorini or Crete, there were also beautiful beaches and streets, but it was plenty of people and tourists that went there to party.
So for me:
Athens was spectacular of course because of the ruins and monuments.
Crete had amazing landscapes and Malia (in Crete) was perfect for some relaxing days.
Santorini has really beautiful streets to walk around them and an amazing sunset.
And Mykonos was beautiful too but we saw it more for partying and having fun!
Super Paradise