I finished my groundschool at London early this year. The truth is, im not totally convinced that where you go is too important. What is more important is that you are totally comitted and willing to put in serious hard work. Nothing throughout the course is terribly difficult to understand, but there is simply a hell of a lot of it!
I was doing between 2-3 hours per night and spending virtually all day saturday and sunday working too. My hard work paid off though, passing all but one first time with good solid grades. This was the case for the whole of my group, which incidentally had about 11 of us. There was one group though that was starting when I left that had about 25, but from what I saw that was rare.
As regards the lecturers, they are ALL excellent and its never a problem asking for extra help. They come from a variety of backgrounds and bring a host of experience to help you.