we are looking to go from Budapest to Croatia in early September. Dubrovnik is high on our list but we haven't narrowed down for sure where we want to go. Any thoughts where to go and the best method of travel? We are hoping for about 4 days or so.
Best method of travel can only be decided once you know Point A and Point B. If you want to save time, flying may be your only option unless you want to focus on the Zagreb area and/or the north. First start by looking which cheap carriers like Wizz Air operate out of Budapest, and which cities in Croatia they go to (preferably direct flights or shortest in duration). Then read up on those cities and see if they interest you (grab a book from your local library). Given your compressed schedule, you have to prioritize somewhat based on ease to get there, so you're not wasting much time in transit and have more time "on-the-ground".
Croatia is quite big, and 4 days is really not much at all. I think Split would be a great place for 4 days because there's just the right amount of things to do there...you can see Split, Trogir, and take a day trip to one of the islands right from Split. If you pick Dubrovnik, then I would suggest a side trip to Montanegro since Dubrovnik is tiny and takes 1-2 days max to see.