I just got back from 2 weeks in Maui.. We went 2 weeks last year too.. Probably my favorite place now. Scuba dived out there twice and it was amazing, you have about 120 ft vis because the water is so clear. We love Maui so much, we bought a timeshare.
Myrtle beach is nice, but dont expect to get good diving; the ocean is brown. But there is ENDLESS activities and places to go/see. Nags head is nice, real laid back atmosphere, along with Hilton Head.
Our next stop this year is a Sandals resort for a long weekend.