Our son was put on 6MP when he was first diagnosed and it really helped him. It did take him a long time to get off the Pred (had to do it 2.5 mg at a time), but he did get off it after about nine months.
He now has anklosing spondylitis and is on Humira, so he's in the process of getting off the 6MP now. We've got our fingers crossed that it goes well.