As a GMAT teacher AND a community college instructor, I also recommend the community college math course. You'll get a lot more of a foundation in simple math than any GMAT course can give you. Even at Veritas, where we have 18-21 hours devoted to math (depending on the course), we assume a lot of prior knowledge. A prep course with only 12-ish hours devoted to math would be even harder!
On top of that, remember: the great majority of the math on the GMAT is not hard. It's the way the questions are asked that is tricky. Once you get your fundamentals down, make sure you spend a lot of time breaking down problems and understanding the tricks.
Jim S. | GMAT Instructor | Veritas Prep