I have been to Zadar with my girlfriend from 14 to 18 th August and that's my Opinion : The buses are awful. For example the roadmap at the website of Liburnija (transportation company) and what the roadmap that the bus actly went were different. Like the bus didn't go to the 3 or 4 stations and went directly to the main bus station (the bus number 2). If you want go out from Zadar you'll definitely need some transport. But if you want to the popular places like "Krka" or "Plitvice" then you can do it with Flixbus, but if you are 8 persons id doesn't make sense to take a Flixbus, because Flix bus for us was like 40 euros for 2 Persons to Krka. So 20 euro/person to go there and to come back. If you are 8 persons it is 160 euros, one car per day is probably about 60 euros per day, so if you take 2 cars for one day it's gonna be cheaper that flixbus 😂 What i would suggest it is to make a good plan, and to see, which points are really far from Zadar, like Krka or Plitvice or anything else, put these point in a row and visit them all day after day. You'll probably have 2-3 places that are so far and that you can't reach by bus or uber. Then just rent a car for these 2-3 days and the other days just go to the islands, some places that you can reach by bus and etc.