We're from upstate NY, about 50 miles N. of Albany, NY. Last December we made it down in just under 20 hours, taking only quick bathroom breaks and eating in the car. Not sure how we managed this, as I drove through torrential downpours all night. Its about 1300 miles each way. Our average time is more like 21 - 22 hours. We've done this a couple of times now, plus a trip to Hilton Head last spring.
We're lucky, because our kids are remarkably good car travellers. Last time they kept asking "are we there yet", but they were doing it to be funny (like Donkey in Shrek 2). Hilarious, huh? All in all, this is how we would choose to travel, unless they start cutting airfares in half.
We're probably going to do this again in October, when we visit Ft. Wilderness (if we have a pop-up or travel trailer by them). I'm guessing that with a trailer, it will probably add on at least a few hours of travel time, as we'll be going slower (like maybe even under the speed limit!).