Halo 4.
Halo's story, lore, universe, environments, music, pacing, weapons, interconnectedness, characters themselves, and so on completely shit on whatever CoD puts out. CoD's story had one moment that got any reaction from me... Back in CoD4 when the nuke went off. Every Halo game had several moments that got me, even Reach. From stepping onto Halo for the first time, for the Aliens-esque reveal of the Flood, punching Keyes in his infected face, to escaping the PoA. Then we played as the Arbiter, killed a prophet, met gravemind, and the covenant upheaval. Then in Halo 3 when we finally stopped what Covenant we knew of, killed the final prophet, and watched Chief get lost to space. Even Reach had the moment where you were left behind, alone, on a dying planet. And then you died.
Multiplayer wise, there is an actual skill gap where the better player comes out with the win. Better maps, vehicles, weapon balance... I think you get the idea.
CoD went stale after its fourth iteration. Halo hit a rough patch with Reach, but Halo 4 has relieved all skepticism I had when Bungie left the franchise.
. H2 and H3 were pretty scrubby.
