That would be Victoria and Alberts.
"Quiet" isn't so easy to come by at other WDW spots, as you'll find kids of all ages at virtually all the other restaurants.
We've found the most quiet (and therefore, romantic) spots to be at Citricos, Blue Zoo, and Bistro D' Paris. But others find California Grill (with that nice view) to be romantic, and there's nothing quiet about the California Grill!!!
But if $$$ is truly no object and you don't mind dressing up for a 2 to 2 and 1/2 hour meal, V&A is by far the best spot.