We were just there a few weeks ago. BEWARE! It was extremely crowded and Roma people were working the crowds. One member of our group (an excursion from a small cruise ship) had his wallet stolen from his camera backpack. My wife's backpack (not camera, just clothes) had her backpack unzipped. Someone told us they would hold up a towel (many people swim at the bottom where many of the falls empty into a river) so no one could see their accomplice unzip the backpacks. It is quite beautiful and I got some nice shots using a 55-200 zoom on my Nikon D7100 (APS-C sensor).

You are in for a treat. Plitvice National Park defies the imagination. It almost doesn’t seem real. We had a wonderful time there in 2009. A 24-105 or 120 would work well. A 16-35 may be nice for certain shots but you may not want to be changing lenses with the enormous crowds that will be there. The walkways over the water get very crowded. The park buses are jammed and too much equipment will be problematic. At the time I used a Nikon 18-200 but now I would use something a little wider. Do all you can to just take it in and don’t let your photo taking dominate your time there. It is simply marvelous. Get there as early as possible in the morning. Lucky you!