The best islands to visit in Greece are Santorini, Mykonos and Crete. But no doubt, any time you talk about "the best", you come to a subjective opinion here. So it is really determined by what you would like, what you are looking for and your personal taste. While these Greek islands may be the most popular, that doesn't always mean they will be your personal favorites.
Greece has as many as 1400 islands, 227 of which are inhabited. Less than 80 of them are home to more than a hundred people.
Do you like well-developed tourist spots? Maybe you prefer ancient history?
Different islands will suit different tastes.
Most of the Greek islands are actually located in the Aegean Sea (between Greece and Turkey), although there are some that are in the Ionian Sea, on the Italian side facing Greece. To get to the islands of the Aegean, you need to get from Athens. This is the traditional hiker's itinerary. If you only have one chance to visit the Greek Islands, this might be your best bet.
Mykonos (near Athens) can be expensive for some. This statement is especially true if you book your holiday in one of the most popular hotels. However, if you just stay here in the countryside it will be much more affordable.
Visitors usually say amazing things about Crete (between North Africa and Greece). The north coast of Crete is the more tourist-oriented part of the island. The south coast, however, has beautiful beaches.
Santorini (north of Crete) is very touristy and very popular. It is great for most people because it provides all the necessary needs for the average visitor.
Paros-Naxos (north of Santorini, and towards the mainland) can provide you with one of the most affordable holidays. It hosts beautiful beaches, historical monuments, architecture and camping.
In the Ionian Sea, Corfu is the most popular island. There are many restaurants, beaches, bars, clubs and culture here.
Also in the Ionian Sea is the very beautiful island of Lefkada, with fantastic beaches, excellent cuisine and at very affordable prices. There is also a bridge that connects the island to the mainland, so you can rent a car and visit many places.