Don't quote me on this, but I THINK Manhattan GMAT
's books are actually Cambridge/Arco's books.
How much studying have you already done? What materials have you already used? In general I don't think weekend courses are helpful because there's too much ground to cover for it to really sink in that quickly. It takes steady prep - master one question type and move on to the next. You need time to apply the principles for one before trying to sort out the next one. And if you need help as you go along, a full-length course is better. Most people taking a course do need help, of course, so I think it's worth it to take a full one.
I used Cracking the GMAT
) and the Official Guide and would give both a big thumbs up. The Princeton Review
tests are excellent and I found the strategies to be very useful and easy to apply (especially when I got nervous and needed to rely on shortcuts to solve tough problems). They have different materials for their course, which I would imagine are quite good since the regular stuff was.