I haven't heard much about South University. I am also looking at online universities right now (for RN to BSN, and hopefully MSN in Leadership and Management after that). I've narrowed down my choices to WGU and University of Phoenix. I'm 99.99% sure I'm going to choose WGU because I will be able to advance at my own pace and it's significantly less expensive. They have so many positive reviews online, and on this website (type "WGU" into the search at the top of the page -- it will bring up all WGU threads). Good luck making your decision!!
My advice is don't. They are a for profit school, their parent company edmc recently had a lawsuit against it by the DOJ for frqdulent student loan practices. It is insanely expensive and they pretty much require you to take all your prereqs over there. I have a BA and a AND and they were making me take basic college writing! Insane.