They are both supposed to be very very nice (out of my price range, so no personal experience. I would pick the Halekulani because I strongly prefer a location right in Waikiki, instead of driving distance outside (Kahala). This may or may not matter to you though.

I've not stayed in either, either , but my wife and I walked into the Halekulani when we stayed on Waikiki a few years ago. Kinda felt like stepping into an oasis, 60 years back in time, and set apart from the relative hustle and bustle around it. Pretty special, I thought. So I priced it, thinking we might combine a stay there with an upcoming trip to Maui. Ummmm......

Are you planning more than just Oahu? The Halekulani combined with a few nights at either of the Four Seasons on Lanai or on the Big Island would make for a special anniversary celebration.

If you want the activity of Waikiki - stay at the Halekulani - but if you want more peaceful/serenity - stay in Kahala, and you are not that far from Waikiki.

As mentioned, the Halekulani is in the middle of Waikiki. It has a small-ish pool and is beachfront, though the actual beach in the area is pretty small. However, it's a short walk to Waikiki Beach where there's a lot more space to lay out. The Halekulani property itself is quite small and compact.

Waikiki offers lots of dining and shopping options and you do not need a car if you don't plan on leaving the Waikiki area.

The Kahala is about 10 minutes away, outside of Waikiki. It's situated at the end of an upscale neighborhood, next door to a country club. The property is beachfront, and much larger than the Halekulani. Generally speaking the atmosphere will be more quiet and serene than staying in Waikiki. If you want to eat somewhere other than in the hotel, you will need a car.

<<<It has a small-ish pool>>>

Small-ish but absolutely beautiful. Google "Halekulani Pool" and click on Images.

We stayed at Halekulani a few years ago. It was nice but I wouldn't say it was spectacular. The service wasn't close to the level of a Four Seasons or Ritz if that's what you're expecting.

The pool is indeed beautiful. The weird thing is that the hedges were so high around the pool, presumably for privacy, that you couldn't see the ocean unless you stood up. You are completely surrounded by hedges. We felt like we could have been anywhere. There was some nice shade around the pool though, which is important to me. We are definitely beach people rather than pool people but the beach was just a tiny sliver and I don't remember there being any hotel chairs on the beach.

We did love the location and we absolutely loved waking up each morning and looking over to Diamond Head and watching the early morning surfers. That part was magical.

We didn't have the cheapest room (nor the most expensive) but it was still very small. The shower enclosure was almost unusable it was so small. We also had a bad experience at the hotel restaurant on our first night and that kind of left a bad taste.

We've never been to Kahala so I can't comment but I would definitely prefer to be right in Waikiki.

Wow with a review like the one above, have you thought about looking at Royal Hawaiian or Moana Surfrider (the two classic historic hotels right on Waikiki)?

suze, we said that when we go back to Oahu we'll probably stay at the Royal Hawaiian. Don't get me wrong. The Halekulani is nice. It's just not as nice as it should be for those prices. My expectations are in direct proportion to how much I'm paying for a room.

You really can't beat the view though. The hotel is right on the end of the curve that is Waikiki and you can see the entire beach area to Diamond Head. It's stunningly beautiful.