Though the island of Oahu is not the biggest in the Hawaiian chain, it offers the widest variety of accommodations. Should you stay in near-palatial surroundings where kings, heads of state, billionaires, and rock stars have spent the night, or in a quaint bed-and-breakfast on the North Shore where the rolling surf lulls you to sleep? Should you choose the bright lights and action of Waikiki or the quiet comforts of Kahala? Oahu has the perfect place for everyone.
The major high season is mid-December to March. At this time of year, rooms are always booked and rates are at the top end. Secondary high season is June to September, when rates are expensive, but bookings are somewhat easier. The low season, with fewer tourists, cheaper rates, and possible "deals" on rooms is April to June and September to mid-December.
Be sure to factor in Oahu's 11.962% tax, and don't forget about parking charges -- up to $25 a day in Waikiki.