Opening a bank account in Croatia

It's not hard at all if you can speak Croatian, Italian or German!  I struggled a bit as a pure English speaker but some branches may have some English speakers.

You'll only need your passport to open an account, but you'll need to decide if it is in Kuna, Euro or both.  Time wise mine were opened on the day (they'll give you a print out with your account details and a welcome pack) -- I had to wait 7 days to receive my PIN and welcome letters, and had to pick up my debit card from the branch I opened it in after 10 days. 

I couldn't tell you of any restrictions, I just have a Kuna and Euro debit account (with online facilities) through Zagrebacka.

As for which is best, it depends on what you're after; I'd look at what's immediately available in the area you'll be in.
Using cashpoints from a different bank can incur charges, different banks will charge different monthly fees, there can be a large disparity between busyness of different branches etc..

Good luck!