Charlestown has a lot to see there are many different tours you can take, and lots of shops. Recommend the Gullah Tour. Charleston has a lot of history. We spent three nights in Charleston and did not even come close to seeing everything. We stayed at The Vendue Inn, parked our car in the parking garage and did not need it till we left. Many sights were in walking distance of the hotel.
Pawleys Island was very quiet. We loved it. We stayed at the Sea View Inn, included 3 meals a day, wonderful food!! See review of Sea View Inn (barefoot paradise)
My husband and I stopped at Georgetown on the way from Charleston to Pawleys Island. Georgetown was a very small town. Has a few nice shops.
Pawleys Island is definately quieter. There is not a lot of "commercialism" there. No high-rise hotels etc. Just mainly privately owned homes. Edisto is more commercial-although not by much. You are about 30-40 minutes from Myrtle Beach as well. I've stayed in both places numerous times-I am from SC-and I prefer Pawley's Island to Edisto. As far as a day trip-Charleston is closer (about an hour and a half) and you can not go wrong there. There is so much to do and see there. Savannah would be my second choice-it's still only about three and a half hours away). Hope that helps.
Seabrook Island is just north of Edisto Island, and is only about a 20 minute drive to Charleston, which makes even nightly trips do-able. We were undecided between Edisto and Seabrook and then finally decided on Seabrook and couldn't have been ahppier. It was absolutely wonderful. I have never been to a beach like it. We found our oceanfront villa on www.vrbo.com and will definitely use again.