I was there for the first time in late Sept. and early Oct. Went to the Cyclades, starting at Santorini and then to Anafi, Paros, Folegandros, and Syros. Great trip with a good photographer and expert on the Greek Islands, Glenn Steiner (www.greekislandworkshops.com
He's been to about 60 of the islands over the past couple of decades and also writes for Lonely Planet about the isles.
For street shooting with my limited experience both Santorini and Syros, landscapes (cultural landscapes) were best in Santorini, Anafi and Folegandros.
In Folegandros, we were there off-season (limited but cheaper rooms, fewer open restaurants, fewer people). I rented a quad and drove around the island and had a blast! Everywhere, the people were nice and friendly.
Lots of good shooting, I can tell you. I was averaging 1000 frames/day.
To go between the islands, best bet are the ferries, but can be hit-and-miss during the off-season and can be cancelled due to the winds, especially the high-speed ferries. If you are flexible, show up and you'll find transportation and lodging with little problem.
I hope to go back sometime and Crete seems to be a good place to try next.
When Glenn and I departed after island hopping, I headed back to Athens and my flight home and he continued to Mykonos and got some nice pix!
IMO, I'd say if you spent a few days on any of your islands, you'll get some great stuff, meet friendly people, eat great food, enjoy nice wine and find a good place to stay!
Check out Glenn's stuff, read the Lonely Planet guide to the islands, plan on lots of time and don't set a hard schedule.
Have a great trip!