I’m considering Cliffs, Barrons, and Princeton.
All of these have mixed views. I’m not reviewing for the AP bio test, just unit reviews. I’m going to buy all three unless you guys can help me out with your valuable suggestions. 
I think Cliff notes is the best book for reviewing the units! If you were taking the AP exam I would also say get Barrons only because they have this section that helps with essay writing. For example, it’ll have a general topic about evolution and then it’ll have subtopics like if the prompt asked you for a cellular evidence of evolution then it would say something about the endosymbiotic theory. Or you can just go to Barnes and Noble and take a picture of those few pages in Barrons but Cliff is the best for review.