Definitely listen to cornfed's advice about taking them for a test drive. I was lucky that my big sib and her friends had most everything there was to use, so I was able to do that. I also scoured Reddit and SDN for how people scored, good and bad, using various books. I eliminated one set right away given that nearly all of the low scores were using them.
After all of that, it ended up that what I concluded after my test drives matched study plans from Koala, Zendabi, Jelly, Nim, and a few others.
For Content Review and Developing Test Skills
Chem and Physics: TBR all the way; nothing else is close (thousands of questions and the best explanations anywhere)
Biology: I used TBR, but there are plenty people who like Kaplan (I needed more review than most having not taken some prereq classes)
P/S: TPR or EK (KA and the 300-page guide are musts no matter what you use)
CARS: TPR or Jack Westin (I used EK and TPR myself, but I wish I knew about JW)
General Practice: AAMC and UWorld (AAMC are the most realistic and UWorld has great explanations)
FLS: 5 AAMC and whichever commercial ones fit your whims