This is so easy:
I have played Halo 3 way way more than COD4
I have played Halo 3 through several times, once on own, once on split screen, once in four play co-op.
I have played Halo 3 loads online.
I have played Halo 3 with EGers online in custom games loads.
Come to think of it I haven't even played COD4 since it came out.
It has to be Halo 3 for me until I get COD4 at the very least, if not before.
I have now bought COD4 - I'm too good for this place, no-one appreciates my talent.
Don't make me angry. You wouldn't like me when I'm angry.