The best way to get to Lahaina is by a direct flight to Kahului Airport , which is the main airport for Maui , then rent a car or take a taxi the rest of the way.   However, it may be cheaper to fly to Honolulu International Airport , and then catch an interisland flight to Maui.    The interisland and commuter terminals are separate from the main terminal, and there’s a shuttle service called the Wiki Wiki shuttle that will take you to either one.

The public bus doesn’t stop at the airport, but most of the hotels have shuttle services.   There are also two smaller airports in Kapalua and Hana , which are used more for commuters and visitors from surrounding islands.   These two airports usually don't have regular shuttle services, but it's usually possible to arrange for a hotel shuttle to pick you up. If not, then there's always the taxi or rental car option.
For visitors who want to explore the area on their own, a rental car is a good option.  The roads in and out of Lahaina are pretty congested, though, and traffic sometimes slows to a crawl during the peak tourist season.  Still, the scenery is beautiful, and it beats rush hour traffic in any mainland city.