My husband and I have been to Santorini and Naxos. We would love to find another island where we can stay at a hotel near the water and veg out. We like to explore so we would love to go to different beaches.
Have you considered Crete. It is very large but has many great beaches.
Fly from Athens to Paros and take the little shuttle ferry from Pounta across to Antiparos.
There is no "best island" All islands have a different atmosphere, and 95% of the inhabited ones have hotels near the beach where you can relax
Ask this question to 10 people, you will get 10 different island names.
Knowing this, the best thing to do is to start by doing research and going to consult for example: