We were very impressed with the process of hiring a car with Sixt in Rovinj, Croatia. We booked a BMW X1 and were very surprised when we arrived and received a BMW X4. The car was very clean and all pre existing damaged was documented to avoid any confusion on dropoff.
The process was very efficient and the staff were a pleasure to deal with. We also dropped in a different location and it was seamless.
One thing to be aware of is they do take a large deposit from your credit card to cover insurance, but this is refunded a few days after you return the car safely.
Definitely recommend using Sixt for your car hire.