Should i get cod waw or pre order halo 3 odst?

Should i get cod waw or pre order halo 3 odst? PLEASE ANSWER ITS A VERY HARD DECISION

I heard ODST is just and expansion and the multiplayer isnt gonna change but a few maps.

On the other hand modern warfare 2 will come out and i doubt anyone will be playing world at war anymore.

PLEASE TELL ME

ODST

I would get neither and just wait for MW2 and spend your money towards thattopher78714