I love what Machichi said! It really does all come down to you.
With that said, you should think about what your needs are on the Quant section. Do you need to review the "math" -- the rules and formulas, etc. Do you need to review the techniques for each type of question and the way to recognize what the question is actually asking? Do you need overall strategy for the quant section and also for not making "silly errors?"
Experts should not really argue much over the rules and formulas! That is the easiest to study on your own in book. With techniques and overall strategy experts may differ. Here is how to know if someone is a true expert...Do they meet you where you are or do they expect you to meet them on their preferred ground? I had a philosophy professor that graduated from college at 18 and had her Ph.D. by 21. She would remember what each student was majoring in and explain each philosophical point for each of those perspectives. Okay here is what this means in economics, here it is in physics, and so on. I have always tried to be like her even though I am sure I cannot match her performance!
A true expert is the one who explains it clearly. Beware of someone who hides behind complexity and jargon. A true expert can explain the same problem several different ways and does not get upset when asked for clarification. One more thing, a true expert should be able to make the difficult seem clearer and the tedious seem almost...fun.
