There's no single "best" island — there's a best one for what you want
This is one of the most-searched Hawaii questions, and the honest answer is that it depends almost entirely on what kind of trip you're after. Here's a direct comparison, not a "they're all great!" non-answer.
Best for: first-timers
Oʻahu. Most direct flights from Australia and the US mainland land at HNL, widest range of accommodation at every price point, most things to do within a manageable radius, and the only island with genuine walkable-city convenience. If you don't know yet which island suits you, Oʻahu tells you the most about whether you want to come back.
Best for: beach resort + real adventure
Maui. Kaʻanapali and Wailea give you the resort experience; the Road to Hana and Haleakalā give you genuinely memorable days that can't be replicated elsewhere. The combination is hard to beat on a single island trip of 7–10 days.
Best for: slowest pace, most dramatic scenery
Kauaʻi. The Nā Pali Coast is the most visually dramatic thing on any of the main islands; the island overall has the least development and the slowest pace. Choose it if you specifically want to slow down, not if you want a packed activity schedule.
Best for: nature, volcanoes, genuine remoteness
Hawaiʻi Island (Big Island). Active volcanoes, black sand beaches, snow-capped summits, coffee farms and stargazing — and far fewer visitors relative to its size. Requires more logistical planning (it's big; you'll want two bases) but rewards it.
Best for: budget travel
Oʻahu, slightly — the widest range of accommodation price points, most competition between restaurants and food trucks, and public transit that can genuinely substitute for a rental car if you're based in Waikīkī.
Best for: honeymooners and couples
Maui or Kauaʻi. Maui has the broadest range of romantic resort options (Wailea specifically) plus the adventure factor. Kauaʻi has the most dramatic scenery and the most genuinely away-from-it-all feel.
Best for: families with young children
Oʻahu or Maui. Ko Olina's engineered lagoons (Oʻahu) are specifically designed for young children; the Grand Wailea (Maui) has the most resort-style family amenities in the state. Both islands have the most options for dining and activities that work across age ranges.
Don't try to see all of them on one trip
The honest advice from our island-hopping guide: one island, done properly, beats rushing across three. If you have 7 days, pick one. If you have 14, two is workable. Three or more in under two weeks is for return visitors who already know what they want.