I used the official ATI TEAS V Study guide, and the McGraw Hill Study guide with practice tests. I found that the ATI book most closely followed the format of the actual test, but that the McGraw Hill book supplemented the ATI study guide's practice tests VERY WELL. I was actually really glad that I used both instead of just the ATI book, because the practice questions in the McGraw Hill book were harder than those in the back of the ATI study guide; the harder practice tests prepared me more for the the caliber of questions on the actual TEAS test.
This is what I found:
The information in the ATI study guide was the most all-encompassing, and the most directly related to the material covered on the exam. The format definitely annoyed me every now and then, because it seemed to jump back and forth quite a bit, but it's worth it because the material prepares you very well for the exam. The practice tests were almost IDENTICALLY formatted to the actual exam too, which I felt prepared me very well.
A friend of mine actually sent me the McGraw Hill book because he said he liked the practices better because they were harder...and he was RIGHT. They were definitely harder, and covered some material not even in the ATI book, and a lot of that material actually showed up on the actual TEAS V exam. I was SO glad I went thru both books.
I took a total of 4 practices tests before I took the real exam, and spent a month studying (I am also returning to school after having completed my first degree in 2007, so it had been a while since I had seen any of the math or science. I'm SO glad I reviewed everything that much).
But I would definitely recommend both of those books. Each fills in the holes the other has, and in the end, I felt very prepared for the exam. (I scored an 86, and a 73 was needed for my program, so I was pretty happy).