Hi Marina,
the answer to your question is very obvious: I LOVED CROATIA. It's one of my favourite corners in Europe and I'm very looking forward to going back in there. What Croatian city are you from by the way??
As for Slovenia, well... I can't give you much information since I went to there on the occasion of a summer university... I did some tour in the country though... the places i visited were Maribor, Pohorije Mountains, Ljubljana, Kranjska Gora, Triglavski Narodni Park, Bled Lake and Skocjan cave - I loved every single place I list in here... Slovenia is a country with a great variety of landscapes, so you must definetely go and check by yourself... you won't be deceived.
If you've got any further questions, do write me : ) bog i sretni praznici u sloveniji!