Prior to Oxford PPL books I tried both the Thom and Pratt books which I found to be very tedious and hard going. I was very pleasantly surprised by the Oxford PPL books. In my opinion they are much better textbooks.
Compared to Thom and Pratt I found that in the Oxford books:
* Concepts are explained well using suitable amounts of material. Explanations are not overly summarised or rushed and they are well paced. The text is well-written and the diagrams are clear. * Presentation is well structured. Information that is presented later builds upon and reinforces information that was presented earlier.
The Oxford books have more material than Pratt or Thom but I actually found them to be much easier and interesting reading than either of the other two.