Ignoring the fact that Metal Gear Solid is a far larger and more popular franchise, it's also one of this generation's most - if not the most - hyped and anticipated game(s). The new gameplay features will also lure new people to the series.
Gears of War 2 will however be released during the holiday period, so sales are definitely going to be higher compared to any other time in the year.
I don't know. It'll be interesting to see which game sells the most. Both will sell enough though...







