I have worked with both. The Stock Market Game allows for more control as far as you are concerned. The only problem is that it is harder for younger students to follow. The VSE Marketwatch is very current. There is only a 20 minute delay in buying and selling stocks (SMG is one day). The SMG does have a curriculum that goes along with their game. You do have to pay a small fee I think (at least in Nebraska), but the curriculum is very good and customizable for grade level.
PS I have some former students that are graduated that still use the VSE to play against each other.