We rent a car for the flexibility and the grocery shopping. There are days it does not get driven, but its there if we need it. We are in Aruba for 2 weeks and like to venture out when the mood strikes.
It really depends on where you are staying . If in the Hi or Low rises there are plenty of buses. They are very convienient, inexpensive and fun
At $175/week or less, we rent a car. We always arrive on Sunday when the cab rates are double and we also like at least one day at Baby Beach. There is so much more to Aruba than the hi-rise area, a one-night cab ride to FFB and another to MJ.
It is a "to each your own" issue, but at least consider a 3 day car rental if you are staying a week. Savaneta, Santa Cruz and San Nicholas all have enough to fill an hour or two before your dinner that evening and your dining experience will be more unique too.
Aruba where the toughest question each day is "where to dine tonight".
we rent a car for at least part of the time, 3 day rental for a 7 day stay, our hotel carts us most places but it's nice to have transportation for when we want to 'just go'
We rented a scooter to tour the island that way in additon to the car, its an awesome way to see the island. The rental prices are very reasonable.