I have both books.
Kaplan is a thick book, but it has big margins big font is is 1/10th as detailed as RR.
RR has no bold and the format just confuses me. Kaplan reads well, explains concepts and only has what they deem to be important (not to many pathways/intermediates).
Both books have tons of pharm integration which is great.
I read kaplan and found that to be fine (havent taken it yet, but I dont run across World/Qbank problems that I cant answer), the sections I read in RR took me forever, but I learned everything about those subjects. I read 1 chapter in RR and then gave up. That being said - there are a lot of great graphs, and picturse in RR, so it's definitely not a bad choice.