While renting a car is the best way to get around Maui, it's also quite easy to use the bus system, taxis, or ride-sharing services like Uber or Lyft. Expect to pay around $40-50 per day to rent a car, and note that parking can be limited in some areas.
If you have extra time, consider a visit to the Lahaina Historic District for some shopping and beautiful old architecture. Alternatively, for those with less time, consider focusing on either the West or East side of the island to maximize your activities.