Statistically, the "easiest" island to get to is Oahu. It has more flights, from more places, and more seats than all the other islands combined. Also, flying into Honolulu is generally cheaper than direct into a neighbor island from most mainland airports. It is acknowledged as the "gateway" to the islands.
How easy is it to fly between Hawaiian Islands?
Flight times between the islands are relatively short – usually less than an hour and sometimes as quick as 34 minutes, such as the Honolulu, Oahu, to Lihue, Kauai, route. Most are direct too, except for the route between Lihue and Hilo on Hawaii Island, which requires a stop in Honolulu.