Renting a Jeep is definitely a good idea. I didn't but wish I had.
It's so fun to explore Aruba and believe me you don't want the fact that you rented the wrong vehicle stopping you from going where you want go. And don't let the road conditions around the hotels, restaurants and shopping areas fool you. The back roads, like in the national park get really rough. You may also see some shortcuts that you want to take, like one we saw to Baby Beach, and not be able to take it because you rented a car. Or like us, you might get halfway across the shortcut, be really worried your tires are going to pop because it's so rough, turn around, go back and take the long way . Not a good feeling
I hope you get a Jeep and be happy.
Renting a car depends on where you are staying and what you will be doing. If your in the palm beach area you really dont need one. If you downtown if might be a good idea so you can get to palm beach, more resturants and what not over there. Or just hit up taxi. If you rent anything I think a Jeep would be the best down here, you can explore more areas that way, the cars are small and would get stuck if you off road it to places.
Rent a car, so you don`t have to wait for a cab, and it is always there,(car), when you need it...And a few trips-here and there, and it pays off. We have usually rental for 2 weeks-about $340-360.....and if you put together all cab rides, then you`ll see a benetit.
As others have said you do not need to have a rental car but it really depends on what you want to do. Taxis are easy to get to get to/from the hotel and airport and to go to resturants. I have rented a car for one day on 3 trips to drive around the island but didn't want to have a rental for the whole time and preferred to take taxis to dinner so I didn't have to worry about driving at night or about having a few drinks at dinner.