I've visited both countries twice in the last 7 years, in both summer and winter. Both are extremely beautiful, Slovenia more alpine, Croatia more mediteranean, tho of course Slovenia is also partly on the Med. In Slovenia, Lake Bled and the Julian Alps are an absolute must, so too is the beautiful, ancient capital Ljublana. (Good pic of Bled on cover of Lonely Planet guide to Slovenia). In Croatia, I only visited the Istrian Peninsula, which, being next door to Italy, is quite Italianate! Handy for popping across to Venice, well worth the journey.

Both countries have very low crime figures, are very safe to travel in, and the people welcoming and friendly. I off to the travel agents...