Honolulu is better when you want options
Waikiki puts you close to restaurants, bars, shopping, tours, and a beach you can reach without planning a full day around transportation. It is convenient for a honeymoon where you want to get dressed up at night and still keep daytime plans easy.
The tradeoff is that it feels busy. If you picture a very private tropical honeymoon, Waikiki may not match that image every day.
Ko Olina is calmer and more resort focused
Ko Olina on the west side has lagoons, resort properties, sunsets, and a much slower rhythm than Waikiki. It can be a good choice for couples who want pool days, spa time, and a more self contained stay.
You will likely use a car or rideshare more if you want to explore other parts of the island.
The North Shore feels completely different
The North Shore is known for beaches, surf culture, food trucks, and a more relaxed atmosphere. It can feel romantic because the pace is slower and the scenery is dramatic, but it is not the place to stay if you want a big nightlife scene.
Traffic can also make driving back and forth to Honolulu more time consuming than it looks on a map.
Splitting the honeymoon can solve the problem
A few nights in Waikiki followed by a few nights at a quieter resort gives you both energy and rest. You can do restaurants and sightseeing first, then finish with pool days and slower mornings.
That can feel more special than forcing one hotel to satisfy every part of the trip.
Choose based on the honeymoon you actually want
If you want to be out exploring, Honolulu makes sense. If the dream is privacy, quiet, and a resort atmosphere, look elsewhere on the island. If you want both, split the stay.
There is no single best part of Oahu for a honeymoon. The best location is the one that matches the pace you want together.