Meridith Bronte wrote this article precisely for this kind of question.
Quote: Maui
Maui beaches are the most popular choice of location among couples looking to taste that “Hawaiian Experience”. Makena is one of the most scenic and beloved beaches on Maui. For garden weddings, the Lao Valley is the famed place. With its gleaming streams, alluring rock formations, and luscious greenery, it is one place that provides an enthralling ambiance fit for romantic weddings. Wailea is home to some of Maui's best luxury resorts, many of these resorts have an in-house wedding planner to coordinate weddings on site.
Kauai
For couples who are looking for that "eco-feel", Kauai is the ideal island, and certainly a beautiful choice for anyone that wants to get away. Kauai, is a quiet place off the beaten path where some of the most scenic beaches and mountains are situated. Many couples planning a ceremony choose Kauai because of it's untamed beauty and lush surroundings. Most of Kauai's buildings are not taller than a coconut tree.
For me, it would entirely depend on the kind of wedding you're aiming for. However for practicality, Maui for the wedding and Kauai for the honeymoon...