Both are on the celerity beyond, and I plan on getting to Italy 4-5 days early to explore different citys. I have never been to greece/turkey or Croatia. I am American and i would not be able to do both for a long time so if you had to pick which ports would you do if you only had one to pick!! need some expertise by people who have done these!
Rome - Messina - Mykonos - Athens - Itstanul - Epheses - Santorini - Naples - Rome
Rome - Olympia (Katakolon) - Corfu Greece - Dubrovnik - Bar - Split - Messina - Naples