I am doing the OAT course and find the books excellent. I also have the Bristol CDROM which is invaluable for its animations.
What I personally have found that is that OAT books are more comprehensive. If you study each chapter and get a good mark in the progress tests at the end of each topic..you're sorted on that subject. I have found questions from other sources easy after studying through the Oxford notes.
That being true for the most part, I have sometimes arrived at a page and found it just doesn't click. I then read about the subject on the web (e.g. wikipedia or the Bristol CDROM) and voila I get it.
If I dare, I would say that the Oxford notes are a bit like reading the Times compared to reading the Sun. One imparts more knowledge with fewer words than the other!
So, in my experience so far I would suggest having a back-up source of material for cross-reference. I expect this holds true for whichever course is chosen.