Which ferry service is the best for Island hopping, should I reserve in advance or when we get there.... it would be from Santorini to Mykonos.
Your choices are Sea Jets and Hellenic Seaways. Both use large highspeed catamaran car ferries. Either is fine. I always tend to go with HS. Usually the're not full, as they're so large, but if you plan to be there between now and the end of August it wouldn't hurt to book in advance online from their website and pick your ticket up at the Santorini port of Athinios about an hour before departure.