Unfortunately, self study doesn't work for most, unless you already have a solid math background and inclination. The problem is the lack of feedback - there is noone to tell you which books to read and which problems to solve and whether you approach the problems in the right and most efficient way. I am a quant tutor and often see students that have self studied resulting in a very non-uniform coverage of the math: some areas covered very well while others (typically more complicated algebra manipulations) still at infancy.
Courses often fail too because of similar reason - lack of personal attention. What they do during the courses is basically read the course textbooks in front of the class and offer very limited private time with a tutor that can analyze your skills and advise you. If you must do a course, because you can't make yourself sit and cover their texts by yourself, choose Manhattan over Veritas. I get students coming to me to improve their math score after a Veritas course way more often than Manhattan which is kind of suggestive. I currently have a student that told me she wished she had spent her money on tutoring than on Veritas and she is not the first case. Manhattan math books are better organized and explained with more details than Veritas. I often use the MGMAT books for students like you targeting intermediate scores. I use Veritas books only as a collection of problems - they are good for exercise but do not come close to the official problem style. One notable exception is the Veritas Combinatorics and Probability book which is the best book written on GMAT combinatorics and probability and the only one you will ever need on the topic. On the other hand, I hear Veritas books are better in Verbal than Manhattan books but I don't tutor that.
The best option for you would be to cover the MGMAT books and consult periodically with a tutor. A good tutor will explain the tough points and swerve you in the correct way of thinking about the problems with his/her custom handouts and huge homework sets to hone your skills - about 100 problems per subtopic is optimal to hit the topic from sufficient number of angles. The prep company that produces problems that are the closest to the official math problems is Princeton Review.
Last but not least, do not make the mistake to not solve problems/practice exams/CAT's under timed conditions. It's completely different from solving them in a relaxed atmosphere. Also do not make the typical mistake to seek a tutor one month, or even worse, a week before the exam. Allow sufficient time, self study, solve problems under timed conditions, consult with a good tutor periodically and the results will come.
