While the original question on this thread was posted a few years ago, it's important to note that students who are considering an online course should sign up for a free trial first. Each student is different so you may find that one course speaks to your needs more than another. Most online courses usually offer a free trial for a limited amount of time, so take advantage of it, and do the research to see which course is right for you.
If interested, you can see how the Economist
GMAT Tutor helps you prep for the GMAT here: http://econgm.at/freetrialoffer
For free GMAT practice questions, follow us @econgmat_qs
Economist GMAT Tutor