I used Kaplan's GRE book and skimmed through Princeton's. I personally liked Kaplan's better because I felt like they explained the answers better. In addition, what truly helped me get my verbal score up from a measly 300 to a 560 by test day (2 weeks later) was Kaplan's 101 GRE verbal practice questions mobile. You can download it from the iBooks app on the iPhone (probably on a similar app on other smartphones) and search for Kaplan books. They have their full books available too, but the 101 verbal questions is the most useful because you can choose which types of questions you want to work on, and they display one problem at a time. Plus, if you don't know what a word means you can highlight it and the definition will pop up in the same application.
For math, if you don't want to drop all the money on taking the prep classes, I would just buy up other people's used books on Craigslist or something like that. I used my friend's Kaplan math workbook from the prep class and thought it was a very good refresher with good tips.
Good luck!