if you have reached F9, it means you have already read some of the textbook from either of them. I read Kaplan always, but recently I bought BPP as well. I find it informative and very good as well.
someone once told me that he bought BPP because of the quality of the paper. ha ha ha it is also true, good quality.
Reading certain textbook with almost same quality IS LIKE BEING IN LOVE WITH TWO DIFFERENT MEN/WOMEN: My advice to you is that, date both text books to see which one you will fall in love with.
its is all about taking risk. You can chose to take high risk and get high return or being save by taking no risk.