If you can spare some extra time why not hire a car in Split and fly back (or vice versa) on Ryanair's new service into Zadar. It is criss-crossed with ancient narrow streets and traffic free. It is a small version of Split heaving with history, culture, art, night life, and delicious food!
Check out TimeOut Croatia for more details.
Šibenik is halfway between Split and Zadar and also has a lovely old town.
It also a convenient base from which to explore the Krka National Park and other places.
Check out TimeOut Croatia for more details.