The question is what are you really looking for?
If you’re into visiting the many, magical islands spread across the sea, then June to August is the best period, keep in mind that due to the global warming effect, the season in many places can be extended to late September or mid-October.
Are you on a summer break? Are you in winter holidays? There are many different options to cover every taste and possibility, as long as you plan ahead and be prepared. A visit to Greece can be a relaxing idea for a limited day spontaneous escape to a tasteful honeymoon destination, providing every option for the traveler on a budget to the ones seeking luxurious vacations.
A breakdown of the key periods would be as follows:
The high holiday season
The high holiday season in Greece is from early July to the end of August, when temperatures are higher, and crowds of tourists, foreigners as well as locals massively, travel to the Greek islands. Keep in mind that you can find warm and pleasant weather during June or September, excellent times for a visit particularly in the islands.
End of Season
Other elements that could affect the timing of your Greek travels have to do with the level of tourism and the amenities provided. Service standards could be poorer under the pressure of high-season, and room rates increase from the beginning of July to September. If you can only visit during the high season, reserve a package well in advance, or plan your journey far from the extremely touristic places.
Out of season
If you are looking for privacy, relaxation and less crowded places, then you should go for the period between April and June. During this season, it will be easier to find budget accommodation and to book tickets for your transportation to and from Greece. Of course, there is always the option of September to late October, as well as winter vacations.