If you don't plan on spending your entire vacation locked in the resort or spending too much money on taxis and private excursions, you definitely need to hire a car in Antigua.
Not only will you save money, you will also be free to go wherever you want, whenever you want, stop at every corner to take photos, go to the markets for groceries and so on. It was thanks to the car hire that I was able to get around the island ad discover The 10 best beaches in Antigua and Barbuda!
Besides, the island is not huge: you can drive from the north to the south of Antigua in 45 minutes.
As I mentioned earlier, I have been to Antigua and Barbuda twice and both times I rented a car through Rentalcar.
Planning ahead, you can find reasonable prices: the first time I paid £165 / €187 for 5 days in total, the second time I paid £230 / €265 for 8 days. These are absolutely competitive prices, compared with the cost of taxis and private excursions.
If you are looking to hire a car, I recommend to pick up and drop off at the airport, so that your car will be immediately available as soon as you land.