Howdy,
I live in NC and I've been to both several times. You'll have a hard time finding a hotel thats not crowded at Myrtle! I would say VA beach is better to take the family. My family goes down every year to Myrtle but we don't stay on the main drag of Myrtle beach we stay a few miles to the south. If you go to Myrtle and stay a few miles north or south it is lots quieter. Myrtle can get wild at times!
There are some nice places on the NC coast and on the outer banks where you can rent condos right on the beach relatively cheap. Those are great places to take the family and vacate. If you want to check those out search for Atlantic Beach, Emerald Isle, or Moorehead City. We were just down at Emerald Isle the first week of May.
Where you live at?