Mykonos is known for its nightlife...we spent a week on Naxos last sept and loved it.

Mykonos, Santorini and Kos are best known for youth-oriented nightlife but by the end of May all the islands will be busy and have some nightlife.

Choose islands that are close to each other so you don't waste too much time in transit between them.

http://tinyurl.com/22wfdvt

Santorini is a given — it has both scenery and nightlife. Mykonos is very pleasant at the end of May. For the third, choose between Folegandros, Naxos, Paros, or a number of other islands. My particular favourite is Antiparos, which is laid back, with good beaches and restaurants, but not much in the way of sightseeing. It has excellent round-island boat trips, which can be accessed from Paros. Late May is still early season, so nightlife will be subdued.

Thank you all. In Santorini, any recommendations on where to stay? I take it that most places will pick you up at port, am I correct? I will look at the other Islands to choose the last one to visit. Also, in Athens, would you recommend a guide, or is it easy to plan things for your self?

We used this company and did their full day tour including the museum. It was excellent!
http://www.athenswalkingtours.gr/index.html

Some places will pick you up for free, many will charge at least €25, some a lot more. It just depends. There is a bus that meets the ferries to take you to Fira where you can catch a connecting bus to whichever village you've chosen for your stay.

If you want hotel recommendations we need to know the name of the village and your maximum daily room budget for the 4 of you, in Euro.

I have looked at Imerovigli which seem to be beautiful. My budget for this Island is 600 Euro for three nights for three people. The sites are not able to give me prices for next May, but I budgeted on late September rates. I will also budget the same for Maykonos. I am not sure where even to begin in Athens. However, looking at other posts, it seems wise to spend the first and last 2 days of our adventure there, in case of strikes, etc. As before, I very much appreciate all the information given. Just so you know, the budget for 3 people for the whole trip, (2 weeks) flights included should hopefully be no more then $7,000.00 Cdn, so I know I will have to pinch a few pennies somewhere. Last year at the same time flights from Canada to Athens return was $729.00 tax in

For contrasts between the islands and accessibility, the Paros-Naxos-Santorini combination (not necessarily in that order) is a great one.

I was around 20 the first time I did that combination and really enjoyed it (still do). It would also help the budget with Paros / Naxos being less pricey than Mykonos.

A couple of years ago we stayed in Atlantida Villas in Oia in Santorini, which at the time had all the wow factor of a caldera view with pool in Oia but without the exorbitant price tag. They might be worth a look.