Halo 2 > Halo 3 > Halo 3 ODST > Halo Reach > Halo CE
Based on campaigns.
I love Halo. Halo 2, Halo 3, Halo 3 ODST and Halo Reach are all fantastic games IMO
I love the campaigns, multiplayer and firefight.
With COD, the only 3 titles i can honestly say i really like are COD 4, COD 5 and MW3. Even then, they lack the creativity and storytelling skills of the Halo series. And the main reason i like MW3 is survival, and I really like COD 4 and COD 5 campaigns.
But Halo 2 and Halo 3 campaigns are enough for me to choose Halo over COD, and I also love Halo 3 MM, ODST firefight and i like everything about Reach.
So, Halo all the way