I can recommend OATs books, they are very easy to read and have good diagrams in them, altho I haven't read any others so can't make comparisons. I also found OATs feedback to be excellent and right on the money, had seen the majority of the questions in the phase 1 exams before. I also found the school exams to be harder then the JAA ones, which is always a good thing. I've only done phase 1 (Systems, Instruments, Met, PoF, Comms x2 and HP) so can't comment on phase 2 yet....