I am currently with CATS 10 done 4 to go and cannot recommend them enough. They have been really supportive and professional throughout. So far I have a 95% average and am no genius but just followed the plan CATS set out. You can always pick up notes off of Ebay or I know CATS now also sell books for the course (£600 I think so cheaper than OA etc).
Good luck with whoever you choose.
Matt