For my family's upcoming Feb trip, the Amtrak AutoTrain is cheaper than flying. Plus we get to have our car with us. We love the AutoTrain and it's like part of our vacation to get to travel on it.
We've driven to Fl many times from CT. It's doable, especially if you have 2 drivers. We always leave early to get through the city early, since you can really get jammed up at the GWB. It's defenitely cheaper than the train and flying, especially if you go straight through. But we find that tiring. It's not unbearable though, especially if you leave at night, drive through, and get there for early evening-then you just go to sleep at the usual time.
Forgot to add, we've often hit slowdowns in Maryland near DC. Once you're past DC, it's pretty smooth sailing (going down).
As a PP said upthread, EZPass is a good idea. I don't have one but might get one-we've spent way too much time in crazy tollbooth lines in NJ!