It is important to bear in mind that, despite Croatia is a small country, it is very mountainous and spread out, specially along the coast.
The price of internal flights can be cheaper than taking a train or bus, especially off-season and off-hours. Whether domestic or international, prices are significantly higher during the summer, so booking well ahead is recommended.
Driving is a great option specially offering independence, flexibility and convenience. Even if public transport is generally good, specially between major cities, getting to smaller towns or off the beaten track and island villages can be complicated. It is worth noting, however, that many old towns and sea promenades are closed to traffic and the lack of parking could be a problem. In case you are renting a car, your will find plenty of local and international companies specially, but early booking is recommended if visiting during the summer. With rental prices starting at €18/day, car rental in Croatia can be excellent value. In general, there’s no particular problem with driving in Croatia and many people drive around Croatia for their vacation each year. To enter Croatia on your own car you will need a “green card” proof of insurance. If you drive a rental car into Croatia make sure that your insurance contract covers travel to Croatia. Some contracts exclude Croatia and other Balkan countries.
Getting around Croatia by ferry in Croatia is both efficient and maddening as you try to figure out the ferry schedule. The vast majority of Croatia ferries are handled by the national carrier, Jadrolinija, and most are car ferries designed to provide a link between Croatian islands and the coast. It is most important to plan out the ferry route before making your hotel bookings.
Travelling around Croatia by bus is an inexpensive option. The internal bus network is excellent on the mainland but buses on Croatian islands are much less frequent. To explore the islands a rental is your best bet. International buses to Croatia are a good way to reach the country, especially from Italy or Slovenia which have few flights or trains to Croatia.
There are not a lot of trains in Croatia but they are comfortable. Taking a train can be a comfortable way to get from Zagreb to Split, for example, saving a lot of driving time. If you are coming from Hungary or Austria, you will find frequent trains to Zagreb from where you can change for a train to the coast. More info can be found on the HZPP website (national rail operator).