If I were traveling to Hawaii with my mid 20's GF, I'd probably want to stay at one of the following hotels.  

1)  Park Shore Waikiki- www.parkshorewaikiki.com
     This hotel sits right across the street from a great stretch of Waikīkī Beach as well as Kapiolani Park.  The rooms are fairly small, but have recently been renovated.  There's a Starbucks downstairs on the corner.

2)  Aqua Bamboo Hotel - www.aquabamboo.com
      This 'boutiquey' hotel sits on Kuhio Avenue, about a 5 min walk to the beach.  The pool area, in my opinion, is one of the nicest in Waikiki.  It's very tropical considering it's located smack dab in the middle of Waikiki, with buildings around it.  The pool is a salt water pool, but please know that salt water pools are not salty like the ocean.  Much less salt in the water.  The rooms with kitchenettes have 2 double beds.

3) Hilton Hawaiian Village Waikiki Beach Resort - www.hiltonhawaiianvillage.com
     For a larger resort feel, this is one of the best in Waikiki.  It has the big meandering pools, sits on a great beach and man made lagoon and has everything you need there as far as restaurants, shops, spa, etc.  There would be more 'people energy' there than at the smaller hotels, obviously.  To walk to the center of Waikiki, it would take about 15 minutes from this hotel.

Hope this helps!

Nancy
Journeys to Hawaii

On Oahu, I would recommend 1. Hilton Hawaiian Village Waikiki Beach Resort, 2. Outrigger Reef on the Beach, 3 Aston Waikiki Beach Hotel.

On Maui, Kaanapali Beach Hotel, Ka'anapali Beach Hotel, Royal Lahaina Resort and Luau

On the Big Island on the Kona side: Hilton Waikoloa Village, Royal Kona Resort.

If you are doing Waikiki, I would suggest the Aston Waikiki Beach Hotel.  Their rooms are reasonable and nicely appointed, and better yet, right across the street from the beach and half mile away from the typical tourist surfing location and shopping.  They offer a free breakfast every morning as well.  One of our favorite bars is on the deck overlooking the beach: Tiki's Grill & Bar.  Nightly music, great happy hour and wonderful bar food...and you can conveniently stumble upstairs.  There on a Friday? Watch the luau's fireworks show from their patio.

If traveling to Oahu, check out Kailua Beach.  There are lots of decently priced B&Bs.  You will be walking distance to the beach. 

Hawaii is a good choice for a getaway especially if you're with a friend because there are lot of fun activities you can do together. And when it comes to accommodations, you will have a lot of options of course.

I always recommend to stay in a villa or a condo, comfortable and at the same time affordable. It gives you a bigger space and will make you feel really at home. You can find great choices here at my company if you want http://www.resorticahawaii.com/ . I suggest you should stay in the The Big Island.This place is considered as one of the most traveled spot in Hawaii

Good luck and make the most of your stay there!