Actually, KAPLAN covers more topics than Cliffs. So, if you read everything in Cliffs, you still need to go back and flip through KAPLAN in order to cover topics like endocrinology, nutrient cycles, etc.
The only reason why Cliffs is a better resource compared to KAPLAN is that it discusses topics in depth and you learn more details; whereas, KAPLAN simply gives you a general overview of each topic. So, read the entire Cliffs book, and then compliment it with KAPLAN.