Hi Seagull88,
You certainly have a lot of books to choose from. Before you get started, it's important to note some things and define your own goals. You and your friend are different people, so you can't go into this process assuming that what worked well for him will work well for you.
1) What is your score goal?
2) When are you planning to take the GMAT?
3) How much time have you set aside to study for the GMAT?
To help you set your own expectations, you should know that most Test Takers spend 3 months (or more) on their studies; during that time, it's common to spend 10-15 hours per week (or more) on the process.
Sometime fairly soon (in the next week or so), you should plan to take a FULL-LENGTH practice CAT. By taking that Test, you can establish a 'baseline' score and get a defined sense of your strengths and weaknesses. A FULL CAT takes about 4 hours to complete, so make sure that you've set aside enough time to take the entire CAT in one sitting. Once you have those scores, you should report back here.
GMAT assassins aren't born, they're made,
Rich