Ok here are some facts, see if it helps you...
At VCD resolution, CQ_VBR gives a sharper picture with less mosquito noise and DCT Blocks. CQ will give you a better bitrate distribution, meaning that there are less (or no) blocks in action scenes. None of these two methods is perfect, and you have to choose which one suits you best.
When there's LOTS of high action-movement in your source I'd still go for CQ instead of CQ_VBR, unless you don't mind getting bitrate peaks of ~3000kb/sec with CQ_VBR to make up for the bad bitrate allocation...
(that would probably be the best method, but you'll need lots of space...)