Which series will be bigger and defining titles for the Xbox 360 ???

if you analyse both games i would say toy story 2

Master Chief is 360's Mario
Marcus is 360's Kirby

i agree with gebx
even tho i like gears better halo always has and always will be bigger

i agree with gebx
even tho i like gears better halo always has and always will be bigger

Well, Halo 3 may not have been the very best that it could have been but Halo is still the daddy purely based on the fact that it has 3 games behind it now, Wether you like Halo 3 or not the game as a trilogy has rightfully claimed legendary status......... So for now Halo is bigger, But once Gears 3 is out then maybe gears will be the new Legend/Daddy...... only time will tell

This even has to be asked?

Gears will never be as big as Halo..ever.

Halo is a bigger franchise , GoW is big but nowhere near Halo...

GoW is growing but Halo is a superstar.  Funny part is most people I talk to including myself like Gears better