First let me tell you that I find odd that Iberia and the Med are all on the same chapter regarding the several cruising destinations: There are probably more sailingboats cruising there than in the rest of the world altogether.
Since Greece and Croatia are on the same bag and I have been cruising there on the last years maybe I can help somebody regarding the choice of their next cruising ground or where they will charter next time (i am talking about summer cruising).
Both are beautiful places but they have their differences.
Croatia is one of the easiest places to sail: Shelters everywhere, lots of Islands at short distance, normally not much wind and when there is it does not last long. In the morning or night there is rare to have wind that starts to blow only after mid day and generally not strong.
Lots of Marinas (between 70 and 100 euros), lots of small city ports (about 30/35 Euros) and lots of buoys with a garbage service included (about 20 euros).
The front water villages are generally nicer than in Greece, there are a big number of old and interesting ones but...they are overcrowded. Excepting the buoys that can also be occupied very early, anchorages are few and everybody starts to look for a place at the beginning of the afternoon and even if you get one you will not be safe because for sure it will come a charter that will drop his anchor almost on top of yours.
The most overcrowded part is central Croatia (Split), the North and South are less. I prefer the South (Dubrovnick and nearby Islands).
Greece is less overcrowded, even on the Ionian that is the region with more sailboats. You will find places to anchor, life is cheaper, few marinas, many village ports (at about 20 euros) and almost no buoys. The Ionian is not very different from Croatia in what regards wind, maybe a little stronger. The Islands are also at close distance, maybe a bit more than in Croatia.
The Aegean is another story, specially in what regards the Islands: less charter boats, less sailing boats but the ones that sail there, even charter have normally better sailors than the ones on Croatia or even on the Ionian...and there are wind, all day, in the night too, even if normally is less strong. Sometimes the wind is too strong and you have to take shelter from some days and also it makes sense to keep an open course and sail away from 20K winds or over.
Incredible places, sometimes the only boat on anchorage, almost always a place to stay on a given anchorage and a different kind of tourism, I mean most places are touristic but in many you will find Greeks, not foreigners, and the cost of life is low.
So, take your pick