Most online courses offer a free trial. I would suggest that you sign up for a few and take advantage of all they have to offer. Each student is different so you may find that one course's features are more appropriate to your style and needs than another. But you won't really know unless you do a bit of research.
Here's the link to sign up for the Economist
GMAT Tutor: http://econgm.at/freetrialoffer
Hope this helps!
For free GMAT practice questions, follow us @econgmat_qs
Economist GMAT Tutor