We chartered a
Beneteau 51.1 with Dream Yacht
Charter out of Lefkas marina a couple of years ago and had a wonderful
experience. There's not much
wind in that part of the Ionian (inland sea south of Lefkada), so we ended up doing a lot of motoring. All destinations are line of sight piloting (1-2 hours from place to place) so it was easy to see a lot of different islands in a week. Yes, Lefkada is ~4 hour drive from Athens, which is a bit of a hassle. This coming summer we're chartering again with Dream Yacht charter out of Athens (Alimos Marina) and will be sailing in the Saronic Gulf (Aegina, Hydra, Spetses, etc.). Alimos Marina is obviously much easier to get to from Athens
airport (~30-40 min drive) and the sailing conditions will be pretty similar to the Ionian (short hops from port to port, lots of options for destinations, pretty tame wind).
I don't know much about the Sporades. The
Cyclades will be very scenic and nice, but longer hops from stop to stop and more possibility of being impacted by Meltemi winds (though it's not as bad in May).
Edit: This was our itinerary in the Ionian.
...and these are the potential destinations we're considering as we're planning our itinerary for this coming summer.