You need to provide a few more specifics In order to get the best advice, and so that we won't waste our time providing information which then proves irrelevant, due to lack of info. Here are my suggestions:
(1) Tell us WHEN you are going (precise dates), and how much time TOTAL you have for the 4 islands you're asking about. Why? Advice can differ greatly depending on whether it's May or August or October, and whether you have 14 days or just 6.
(2) Get a guidebook for heavens sake. U are spending big $$$$ on this trip, don't go all cheapo and balk at $15-$20. Trying to get all your info via internet is like trying to get a drink from a fire hose; you drown in it and are still thirsty. U can even buy used guides online for $5-10; (2014 editions not necessary, you're looking for overview, not the latest price updates for dining & rooms). You can even go to the library. Since RS doesn't cover islands, I suggest Rough GUide to Greece, next fodors if u are wanting upscale. We can give input & help u choose between places/hotels, but you need to do homework too.
(3) If u want the "best beach" and "best Location" you sound as if you have an ample budget, but how can we know what level you want/expect. You need to supply the range you're prepared to spend for a night's lodging -- and in Euros, please; most quotes are in euros, and if we're giving advice it helps if we don't also have to do the converting. Here's the best & fastest conversion site: http://www.xe.com/currencyconverter/
(4) As for location, it helps to know if you expect to rent a car for any of the islands, or prefer to manage mainly with local transportation. This is key, along with the time you plan to be there. These things matter.
… as a start, while you're getting a guidebook, here's a good overview site for the Cyclades: http://www.greek-islands.us -- it's not really "US" it's by a greek schoolmaster, well-organized, noncommercial, and it gives quick, visual thumbnail profile of the islands you list.
-- I'm familiar with all the islands you list, and will be happy to make recommendations on all 4, once you've provided more facts, AND done a bit of homework so we don't have to provide all the background (such as, sometimes the "best" beaches do not have accommodations bordering them).
Your trip sounds wonderful, and with a bit of planning it can be perfect… happy planning to you! -- TJ