Be sure to ask the agent when you check in to pick up your car. Limo Service is an excellent way to get around - provided it is within your financial means. Prices vary of course, but in general you can rent them by the hour, day, or even week. Be sure to ask the company about their options. To travel short distances on sunny days, motorcycles can be good fun.
Mopeds have all of the same considerations as motorcycles with a few more.
First of all, Mopeds are not motorcycles, nor are they bicycles. They require the rider to exercise immense caution. Normally their top speed on level ground is about 35mph and they are quite underpowered going up hills. Since there are a lot of steep hills in Hawaii you need to know the topography of the areas you plan to traverse. Therefore, if you plan to rent a moped, anticipate that you will use it for short excursions and plan to avoid moped trips that will take you long distances or up country - and exercise extreme caution, especially in traffic.