I predict Halo reach will have best sales in 2010, while GT5 will have best lifetime sales. If nintendo decides to change Super Mario Galaxy 2, to Super Mario Galaxy Wii though, it will be well on its way to becoming the next 20mil+ seller and utterly crush both halo reach and GT5 sales combined.
My predictions
Halo Reach:
Week 1: 4.5mil
LTD: 11mil
GT5
Week 1: 2.2mil
LTD: 12mil
Super Mario Galaxy 2
Week 1: 1.8mil
LTD: 9mil