GMAT Quantum. This guy explains problems in soo perfectly. He doesn't just tell you what to do, he takes you through his thought process which is huge. He has really helped in my quant preparations. Once I finish my GMAt I plan on posting a thread on him or at least mentioning him in my "GMAT Experience" post. I don't even remember how I came across is site but I feel like others need to hear about him.
ohh.. and I probably should mention that I have paid for both services but after using GMAT Pill
for a few videos I stopped using them. In an effort to not sound too negative I'll just say it wasn't for me.