I have been using 2 GRE Prep Material and so far each one have been very helpful with my GRE Preparation.
Magoosh - overall, it has helped me a lot! Given that I had purchased a license at a discounted rate, the contents are also very much helpful in helping me remember past lessons
Preped - Although this prep program is still new in the market, their courses are really challenging. Also, I got the chance to try some of their tests for free...just wanted to try it out before actually purchasing their full course. Did not regret spending a single penny on this!