Greece rocks for Kiting! I spent some time there last July.
I kited Paros and Naxos both were great, I had 20+ knot days every day

the only days I couldn't kite were the 35+ knot days

those are the days when you explore the rest of the Island just be careful not to get blown of yer scooter

On Naxos the place to kite is Mikri Vigla a great bay about a 45 min Scooter ride south of the main port. It is a Kite surfing mecca unfortunately it has been well discovered by the German/Austrian/Swiss pole surfin Motorhome owning crowd they have been going there for 15 yrs, so can get busy. As far as accommodation is concerned you have a few options, the Taverna owners allow you to camp on their land as long as you eat a meal there each day, you can also camp for free in the sand dunes like I did which was great fun or there is pretty cheap accommodation which you can organise online before or just turn up, this is the cheapest way. There are two kitesurfing schools there, I know one does rental gear and has accommodation I think they are called the Flisvos Sporting club or something like that.
On Paros you need to head to Pounda a 10min scooter ride south of the main port,the wind was also cranking (Paros and Naxos are neighboring Islands) the water was a bit flatter as it is sheltered by Antiparos Island about a 5min Ferry ride across the bay. You can easily stay in the Port town which is cheap and very nice, wait till you get there before organising accommodation it is super cheap 25 euros for a nice double room was the most I paid. I think Paros might be the better choice as there is good night life too. Definitely hire a scooter to get around only 8 euros a day remember you must barter!!
I went to Sardinia at the end of August, I stayed in Porto Pollo on the North east of the Island. Another Euro mecca that has been discovered by the Germans etc. There is an Island there called Isola dei Gabbiani it is at the end of a sand bar spit that splits the bay in half, Pole surfers on one side, Kiters on the other. Most of the accommodation is on Isola dei Gabbiani it has camp grounds, Donga's and bungalows, it gets busy so you will need to book ahead! A very nice place, the wind wasn't as consistent as Greece, I had a lot of windless days there. You will also need a car to get around, you can then explore to the North as well which has some great wave spots I think from memory the best was Santa Teresa.
In summary, Greece cheap beautiful, windy and great food!!!, Sardinia a bit quieter not so much wind and a bit more expensive both would be great for Learners through to Advanced. My pick would be Pounda on Paros :) I am a little bias though as 2 weeks of my Sardinia trip were spent lying in my tent on the beach with the worst food poisoning I have ever had

I did have a good view though as I lent out of the tent to throw my guts up. Sorry bout the long winded response, I could talk about Greece all day I loved it so much.