What do you like to do on vacation?
As I mentioned we LOVE Fripp as a vacation destination. But it is definitely the opposite of Myrtle Beach.....no resturant choices to speak of, no theaters, mini-golf, amusement parks, video centers or outlet malls! And a whole lot less people.
On Fripp there is LOTS of wildlife, beautiful bike paths, golf car rentals & 2 golf courses, playgrounds, a kids activity center, swimming pools & the BEACH. For your group...the beach, the pools (make sure you have access), riding bikes and golf carts, playing golf, and seeing the wildlife.
As for Hilton Head we like to stay in SeaPines and I enjoy that area very much as well. But I like it for many of the same reasons....beautiful bike paths, golf courses, playgrounds, swimming pools, and the BEACH! There are ALOT more restaurants, some shopping areas, a nature center, and more people at Hilton Head. You'd be MUCH more likely to rent a home in Hilton Head with a private pool for your group - which is something we like (unless we're at an ocean front condo).
From either destination I'd make sure to do a day trip to Hunting Island. And perhaps into Charleston.
If your group loves beautiful beaches either location will be great....check out VRBO and other internet rental sources for a perfect location & great deal.