Maui is the place for certain. Sure it's more expensive but it's clean, not full of kids and you can get some great meals inexpensive if you look and ask around.
Maui Sheraton has the best beach up against Black Rock, you can get all the great tours there and again you must look around to get the best deals. Do not and I mean do not buy any tours from your travel agent. It is cheaper there and there are tons of place that you can get great dinner cruises I recommend the Spirit of Lahaina.
I also recommend doing the tour The Road to Hana, it's an amazing trip, last all day and you do a lot, see a lot and have a great time.
The Maui Ocean Center is a wonderful place and totally awesome. You'll love it for certain even if you aren't a water lover. What you see there is truly one of a kind.
Don't eat at Pizza Hut unless you want to pay $19 for a plain cheese pizza, be sure to take advantage of Whalers Village there's an ABC store there and they always have a special on water. Take advantage of it. Also there's a Safeway 5 miles down the road .Use it as well.
For car rental get a convertible or jeep, don't get anything else. Trust me on this, it's worth the money and the amazing views you'll have are priceless.
Now if you want to get an eye full, head on down to the Big Beach and just happen to wander to the right of the beach where you'll find a beaten path that heads straight up. Take it and once you hit the top look to the left and see a great view of the big beach. Look to your right and you'll find the Little Beach which is the nudist beach. Make your way down the hill to the little beach, find a spot in the middle towards the back, leave your sunglasses on and view on my friend.
Just be sure not to make it to obvious, you'll love when the hot chick shows up in front of you and bends over as she's taking off all of her clothes. Bring a newspaper as well, it makes for good cover of your parts if you feel a little awkward.
All the people aren't hot looking, there's a lot of older folks but there's a good share of the hot looking chicks.
I can go on and on but if you don't choose Maui, well you're going to miss out on a great time and likely spend it in some place you are going to wish you went to Maui instead.
Do yourself a big favor and look at the Sheraton Maui website and they always have specials. Look at them all, some come with a car, some with free breakfast, some with both.
If you can get the free breakfast deal, take it, because breakfast buffet there is about $18 and has everything under the sun. Trust me, if you get breakfast for 2 free everyday during your stay, you'll never eat lunch and only shell out for dinner. You can get a good dinner for under $10 a person right down the street from the Sheraton.
Have fun and enjoy your trip no matter what any of you that are going decide.