I haven't stayed at either of these downtown Marriott properties, but from experience I'd say the Courtyard is less expensive than the Renaissance, and also the Courtyard does not usually provide a full-service dining room, or concierge room for Gold-Platinum members. If you're one of the latter card-carrying members, you're more likely to receive a room upgrade at Renaissance than Courtyard. Both hotels are quite accessible by foot to most of the downtown attractions and restaurants, except the Citadel Military Academy.
While in Charleston, take the time to drive over to Sullivan's Island and drive around to see the quaint summer cottages, tour Ft. Moultrie and eat lunch at Poe's Tavern (shown here). There are numerous fine restaurants in downtown Charleston, but one of our favorites for lunch is Fleet's Landing, a good hike from the Courtyard or Renaissance.
Hey conlon! I, sadly, have never visited Charleston, so cannot speak from personal experience. I have, however, posted a few past threads below, which contain some of the other Insider's experiences with properties. Hope these help!
We had a wonderful time in Charleston in December. We stayed at the Charleston Marriott and it was a major disappointment. I would definitely stick with the two properties that you mentioned. If you are gold or platinum stay at the Renaissance, for the breakfast. If not, then it's a tossup. both are nice hotels in excellent locations.
While there, make certain that you take the Gullah tour of Charleston. It gives a different perspective than all the other tours.
SNOB is a great restaurant for southern food. Halls is very pricey but a wonderfully elegant experience with excellent food and service.