Having sailed most of it in our own boat
Ionian - way to many charter boats who have no idea what they are doing and very crowded.
Aegean -- lots of great islands to visit and not to many charters but not as many
anchorages as you may wish. But if you are on a short schedule and get caught by a meltemi starts blowing and stays you may not get around a lot of if you do it is a bash.
Croatia - lots of islands and nice folks, good
history and places to
anchor and enjoy. If in
Croatia try EuroMarine in Dubrovnik for charter. They are a
Jeanneau dealer and we had them do some
work with us on a couple of issues we had and we watched as they took care of their fleet and we were impressed with way they maintained them.
Turkey - we only sailed a bit so far - but
anchorages everywhere, great protection from the meltemi and the blows are nothing compared to
parts of the Aegean.
Montenego - to small - a few days and you have seen it all.
good luck