i've been to all of these countries except albania (hope to be there in 2 weeks and with no hesitation would choose croatia. by far the most beautiful one of them, where plentiful charming historical cities are accompanied by absolutely stunning landscapes and one of the most picturesque coastlines in europe. plitvice is the most beautiful national park ive ever seen, dubrovnik is one of europe's top most charming small towns, hvar is second most beautiful island ive ever seen
bosnia is also nice (mostar is great, sarajevo too) but it has no coast (besides the 6km stretch in neum, which i found ugly).
and serbia is by far the least interesting for me - no mountains like in slovakia, slovenia or bosnia, no coast like in croatia. just a flat rather monotonous agricultural country with cities which really dont stand out compared to any other european country.
I have just spent a month between Croatia and Slovenia. Both countries were totally amazing. The landscapes are breathtaking, Ljubjana is small and pretty but has so much to offer, culture, night life and shopping. You must visit lake bled for a few nights, I cannot explain how beautiful it is. I travelled to most of Croatia's main spots, my favourite was Dubrovnik as it was so historic, although it was very touristy. Go to the islands I loved Hvar, Brac and Korcula which has turquoise blue lakes in the national park, that you can swim in. From Dubrovnik you can go on day trips to Bosnia etc. If you do travel in Croatia my advise would be use the buses rather than trains they are much faster.
Hope you have a great time where ever you go. Mel x
Thanks again everyone, very good info. Very helpful.
Albania is going to be on my list, but otherwise not sure yet.
Bosnia,Croatia,Slovenia & Serbia.....
At the beginning I have to write I'm glad you enjoyed in Slovenia... I agree - it's small but various country.
Otherwise, If I had to choose 4 I would pick Slovenia, Montenegro, Croatia and Albania.
Since I've been to all the countries you mentioned, including Macedonia I'd give my vote to all of them. However, I must say I prefer Slovenia and Croatia because they're so close, you can enjoy both of them in a week and get the perfect balance of amazing lakes and mountains in SLovenia and breathtaking coastline and sea (also beautiful rural sites) in Croatia. If you don't like tourists that much, you can always go to places like Kornati, little Istrian villages in Croatia and enjoy the serene environment.