Just to let you in on how I ended up planning this whole crazy trip... About 11 months ago we decided to spend the rest of our Delta miles. So we decided to do the one day layover in Paris because we loved it in the past and wouldn't mind seeing and doing a couple more things. The main part of the trip was Greece. But since we were allowed one stopover, we decided to make it Rome, since I've never been to Italy.
Unlike past vacations, we tried not to splurge too much on higher end hotels. We actually stayed at none that were more than 3 stars. But, all the hotels had to be clean, safe, close (emphasis on clean).
As for how we decided on Zakynthos and Santorini... Santorini was a no-brainer and was always in. Mykonos from what I've heard and read was not really our thing this vacation - cosmopolitan, expensive. We originally were thinking about other islands like Paro, Naxos, and Crete, but after finding pictures of Zakynthos in all of the magazines and travel books, we decided, hey why not check both seas, the Ionian and Aegean. I'm glad we did.