Hey mustafa, some of these guys are joking.
Look, my opinion:
If you want to see the island and see the remote parts like es vedra, "hidden" beaches, small towns and really discover the quaint folksy and more rugged side of ibiza then rent a car.
If your aim is just to go clubbing then just bus it bro!
You can always take a taxi too. As to the planning of your trip, which night are you going to?
It helps if you find people with similar interest.
I am just trying to help.