Another vote for HHI here, however I have never been to VB to provide a comparison. We try to spend a week at HHI every year, usually in the off season which is easier to get if you are not a owner. We have a 9 and 2 yo and there is plenty for both to do on and off the resort. On our last trip my DD and I decided to try the kayak trip offered thru the resort and had a great time. We always bring our own bikes and enjoy riding all over the island. My DS had a great time riding his tricycle all over the paths throughout the resort. In addition, I agree that the CMs at HHI are great and the resort offers many activities for the children throughout the day (some for a small fee). Some of my DD favorites are tie dye, messy science, pin boards and of course Goofy Bingo.
In addition, many people enjoy taking a day trip to Savannah which is about an hour drive from the resort. If you are unfamiliar with Savannah you can park at the visitor center and catch a trolley tour which will provide the history of Savannah and makes multiple stops throughout the city where you may get on and off to explore on your own. Another nice day trip is to Beaufort, SC, and the Hunting Island Lighthouse.
No matter what you decide I am sure you will have a great time.