I’ve been to Maui four times (including my honeymoon), and Kauai twice. Both are amazing, but I think Maui is the best bet for first timers like you and your fiancee. Maui’s a little more tourism-focused, and gives you more of that “Hawaii-like-you’ve-seen-in-the-movies” experience.
These would be my recommendations:
Staying in Kaanapali is the best, but it sounds like it’s out of your price range. Kaanapali is a string of resort hotels connected by a boardwalk. My favorite is the Hyatt Regency, but it is pricey. The Royal Lahaina Resort is cheaper, though even that might still be out of your budget.
But even if you don't stay at the Hyatt, try to have breakfast one morning at their hotel restaurant called "Sonz at Swan Court." It's an amazingly delicious breakfast buffet in an open air setting with a lagoon and swans. You'll love it.
You can walk up and down the boardwalk to enjoy the views, and stroll through the other resorts. Right in the middle of the boardwalk is a mall called “Whaler’s Village.” Lots of souvenir shops, restaurants, and clothing stores.
Right next to Kaanapoli is a small town called Lahaina. This might be a good town to look for hotel rooms. The hotels are much more modest here, but the prices are better and the location is still ideal. Lahaina is a former whaling town that's now a tourist mecca of great shops, restaurants, and art galleries. All the restaurants have amazing views of the ocean at sunset. For a cheap (but delicious) meal, go to Cheeseburger In Paradise (no relation to the Jimmy Buffet chain restaurant). There’s a giant Banyan tree park along the marina with a small Lahaina History Museum, and on certain weekends that have flea markets and art shows under the tree.
On your first day on Maui, go to Snorkel Bobs on Front Street in Lahaina and rent snorkeling gear for you and your girl that you can keep for the whole week you’re there. You'll get LOTS of use from that gear. Two can't-miss snorkel spots: Black Rock on Kaanapali Beach, where you'll almost certainly see some big sea turtles, and Honolua bay, just a 15 minute drive from Kaanapali Beach. Lots of sea life there. My wife and I even saw two small octopi there last year. If at all possible, make sure to have an underwater camera with you that takes both photos and videos.
You can also take a snorkeling tour out to a place called the Molokini crater. Supposedly, there’s a great variety of fish life out there to see, though when I went there last year for the first time, we didn’t see many fish. Maybe we were just there on a bad day. But we did go “snuba” diving, which is just what it sounds like: a cross between snorkeling and scuba diving. Anyone can do it with ten minutes of training, and it was a lot of fun, even if we didn’t see much sea life. If you plan a Molokini snorkel trip, make reservations at least a week in advance if not more. I think the prices were around $100 per person.
For a really fun day out, go to Mendes Ranch, on the opposite side of the island. There you can take a horseback tour along some mountain ridges and down near the water. (Again, you'll need reservations). If I recall correctly, a horse ride is about $135 per person, and lasts about 90 minutes.
People will tell you the most AMAZING meal you can have on Maui is at "Mama's Fish House." Me, I've only been there once and didn't care for it too much, but then I’m more of a burger and fries guy. Also, it’s damned expensive, so I would skip that (though again, bear in mind that everyone else in the world loves that place for whatever reason).
My favorite activity on the island is also the only one that’s free: the Road to Hana. It’s an amazingly scenic, all-day drive with lots of fun stops. (But if you go, don’t make the mistake I did once and get a late start. You want to hit the road as early in the day as possible, or else you wont get back until after midnight.)
For the Road to Hana, pack your swim trunks and a towel, then drive first to the town of Paia. Pick up a CD to narrate your journey, along with snacks and drinks for the drive (there are very few chances to stop for food along the way). Then follow the CD, and stop as often as you can. There’s plenty of great little hikes, viewpoints, and other neat places to pull over. You DEFINITELY want to stop at “Twin Falls.” It’s about a half mile walk, but at the end you’ll find a beautiful lagoon with two magnificent waterfalls where you guys can take a nice dip.
The road to Hana will be crowded with tourists, but don’t let that stop you. You’ll drive over many one-lane bridges where the honor system applies: first a few cars pass going one way, then someone has to be cool to stop and let a few cars go the other way.
Once you get to Hana, stop and marvel at the cool black rock beaches, and buy a souvenir from the famous Hasagawa General Store.
Despite the name, the Road to Hana doesn’t end in Hana. Twelve miles more and you’re at Haleakala National Park, with their “12 Sacred Pools.” (ignore the name – there’s something like 26 pools there.) The views are great, and you’ll top off your day with a nice swim. Then, turn around and drive home, enjoying all the same sights again from the opposite angle as you return.
On another day, you might also enjoy a drive up the Haleakala volcano. It’s 10,000 feet high, and you can hike around the rim of the volcano a bit.
For a truly memorable experience, go to the top of the volcano early in the morning to see the sunrise. To do this, you need to wake up around 2am, make the 2 hour-ish drive up the volcano, stake out a good spot along the brick wall facing east, and enjoy the show. If you get there early enough, you’ll see an unbelievable view of the night sky, with billions of stars and colored streaks through the sky. But (I cannot stress this enough) DRESS WARMLY. It is cold as BALLS up there in the morning. A sweater and ski jackets at the minimum, plus a heavy blanket to huddle under. And coffee. Definitely bring coffee.
Lastly, you can’t go to Maui without seeing a luau. I recommend the Royal Lahaina Luau in Kaanapali. The location is ideal, with a theater right along the beach, and it’s actually a little less pricey than some of the others. For a small extra fee, you can get front section seating to really enjoy the show close up.
So my suggested itinerary is:
SATURDAY: Land at airport. Transport to hotel. Explore resort, and unwind. Eat dinner anywhere in hotel or along Kaanapali boardwalk.
SUNDAY: Relaxing day. Enjoy your resort’s pool, and/or go to Black Rock Beach and soak in the rays, plus do some snorkeling next to Black Rock. For dinner, go to Lahaini. Allow enough time to walk up and down Front Street and window shop.
MONDAY: Mendes Ranch in the morning for horseback riding. Then back to Kaanapali in the afternoon. Maybe head over to Honolua bay for afternoon snorkeling. Go to bead early that night in preparation for…
TUESDAY: Wake up at 2am. Head to top of Volcano. See sunrise. Back to the hotel by noon for lunch, and spend the rest of the day at the pool.
WEDNESDAY: Relaxing day. Chill out at the beach or pool. Take a break for lunch at Whaler’s Village, where you can check out all the shops. Royal Lahaina Luau that night.
THURSDAY: Wake up early for the Road to Hana. Hit the road no later than 7:00 am. Don’t forget the swim trunks and towels.
FRIDAY: Scuba trip out to Molokini Crater. More snorkeling/beach relaxing in the afternoon. Have dinner that night in Lahaina, or somewhere along the Kaanapali boardwalk.
SATURDAY: One last relaxing day. Spend some more time in Lahaina, and check out the Banyan Tree art sale, if they’re having it that day. Enjoy the afternoon back on your beach or pool.
SUNDAY: head home sunburned and broke.
These are my recommendations, based on my few trips to Maui. I’m sure you’ll get many more suggestions from lots of other island lovers. But if you’d ever like to pick my brains about these activities or anything else Maui related, feel free to message me anytime you like. Congrats on your upcoming marriage. Have a great honeymoon!
