I did Kaplan biochem and EK biochem. Kaplan was WAY more organized, detailed, and understandable. I like how EK stresses the general concepts that we need to know but it really feels disorganized and hard to follow. New information is presented one after another and there isn't a lot of examples, or clear explanations to provide an in-depth understanding of the material. With that said, Kaplan doesn't have the 30 minute passage based tests so EK definitely wins over there. EK is also not following AAMC's outline whatsover, and if it is , it's very very disorganized. Kaplan biochemistry chapter 1 follows the AAMC outline word for word, explaining each topic in their respective order. I found it so pleasant, and was able to follow each topic with khan academy while doing kaplan.
I'm doing both full sets so it doesn't really matter, but if you had to go with one, I'd say Kaplan would be a better choice.