First question is how long are you going to be sailing for? One week, two etc...???
If you are on charter
be mindful that you have to get the boat back to its base at the end of the trip and you do not want to be bashing back if the weather
turns. End of May is a lovely time of year to be in the Cyclades though, the Spring storms should passed and the Meltemi is not yet in full swing.
If it were me and I had a say 10 days from Paros returning Paros I plan a circular route
taking me into the prevailing N'lies NW'lies in the first part of the trip and then returning with them at the end.
So maybe Paros, Anti Paros, Despotiko, Sifnos, Serifos, Kinthos, Naxos Paros??
If you can get up to Kinthos then a visit to Sand Bar Bay is worth doing as there is a nice taverna between the bays and in the west bay there is a neat hot water
spring on the beach that has been built up with rocks into sort of hot tub.
Siros is also nice and could break up the trip back to Naxos / Paros.
But the main thing for me is not to end up having to motor
back north at the end of trip into a gale, saw a lot of boats having to do this and it did not look like a lot of fun. With the Cyclades it is important to have a very flexible itinerary that you can extend or shorten as the weather dictates.