Janni is right, and Rich is also right.
VIR usually becomes everyone favorite. It's big and spread-out. The hills, blind corners, fast straights, and the scenery are all fantastic. You run a large portion of each lap with the gas pedal flat! I want to retire in the area just to run this track often.
Sebring is big, as in 3.7 miles and 17 corners long. You have to have the track memorized to get up to speed. Except for the 2 straights, you spend most of your lap turning. It is flat, and that helps but it is also bumpy. The bumps don't hurt us street cars any, it just adds another element the smooth tracks don't have. It is O.K. to learn Viper Days here, I did. You just have to LEARN the track and stay within your cars abilities. Get a good instructor and you will be fine.
They are both great in their own way. Do both if you can. Sebring will make you faster for VIR.