I took some online courses for my undergrad through the UT system. I liked that I did the work on my own but still had deadlines. The teacher was available whenever I needed her.
I also enrolled at MSU but I hated their online program. It was very difficult to use and the teacher never responded to any of my emails.
I personally haven't taken classes from Pheonix, but I am considering it as well. I have many coworker who like it and have successfully completed their programs. I haven't heard anything negative so far.