I am planning an 8 day trip to Slovenia and Croatia in September and am running out of time to do the things I want to do. I am currently planning to start in Ljubljana with side trips to Lake Bohinj, Kobarid and Postajna. In Croatia I plan to go to Motovun, Rovinj, Pula and Opatija. I am flying out of Zagreb to go home and was wondering if I should spend my last day on the island of Cres or at Plitvice. Any advice would be appreciated.
Thanks!

Go to Plitvice, no doubt. The only issue is where you pick up and drop off the car,it will cost far too much to drop off in a different country.

Second Plitvice, the hiking in the park is most enjoyable.

to get to Cres and back in one day may a problem re: transportation.

dont know cres

i liked plitvice and im glad we went
we went there first before heading to the coast
it was the only inland destination besides zagreb

it is beautifully set out with the boardwalks and can be rainy so bring a good raincoat

i dont know that id do a whole day there though
we spent a morning and left by midday for zadar and then trogir

we stayed right in the park and were upgraded tothe best hotel there ( it's not wonderful but quite pleasant and the breakfast spread was good - very attentive waitresses )

there are a lot of easy walks you can do but we were limited in choice cos of the heavy rains in the previous days which makes some areas of the lakes off limits
a couple of hours were enough for us

however beautiful it is, there is a sameness about it too
you get the picture and so you dont have to spend days there unless you really just want to chilll out while walking

definitely worth a visit to balance what you see on the coast
watch out for the cute flat snails on the boardwalks

Do not miss Plitvice! I spent two nights there, and could have stayed longer. It is unique. I haven't been to Cres but I went to Hvar and would take Plitvice over Hvar any time.

As Danon said, transport to/from Cres for just one day may cause problems.

My vote is for Plitvice as there is really nothing else like it. It would be a wonderful last day. Even if it were to rain it is still lovely.

If I was given the choice, having been to both, I would definitely choose Plitvice (there are prettier islands than Cres).

Thanks, everyone!