This was my reply to a thread on a gfx forum I co-run...
"The time has come for me to list why I voted for Halo over CoD
Although i'm not a great MM player, & i'll freely admit that. I still prefer Halo over CoD.
As others have said, in many respects they are both very different games. Not only visually, but how they play & what they have to offer the player. For me, Halo 3's ranking system was a challenge. But it was a challenge that just kept me coming back & chasing that high rank. It rewarded you for doing well, as did Halo 2. While I can appreciate that the set up for ranking in CoD is a completely different concept, it never really held my attention. I knew that no matter how bad things got, I knew I was still going to lvl, but it would just take me a few extra games is all.
The campaigns, although completely different to each other again. Halo just has so much replay value for me. Not only in single player, but going though in co-op has always been a lot of fun. Halo has a rich story driven aspect that just isn't there in any of the CoD games, except for maybe WaW.
The Halo campaigns all tie to each other to build up one big story, which is another thing I find very appealing. Even though individually they may have their flaws, when you put them all together, they build up to one of the best saga's out there. Add the novels to the mix, & you'll see why.
Although i'm not very familiar with the back stories to the CoD campaigns... as far as I know, they offer nothing similar to this. But please correct me if i'm wrong.
Another big draw for me on the Halo games, was the addition of Forge... I can create & play on any map I have made, or my friends have made. From time to time, the good maps will be added to the MM hopper in MP as well. Some of the community created maps are very good, & in some cases, better than the shipped maps.
Firefight is one of my favourite game modes. It has a lot of appeal in its Reach form. But for a true "Balls to the Wall" experience, there will be nothing to touch the FF in ODST.
Again... these are two things that CoD just can't offer. However... I can appreciate (as others have already said) the ease of just being able to jump onto CoD for a bit, get my MM fix, then leave
My reasons might sound a little bias to some of you... but i've never hidden the fact that i'm a Halo fanboy lol"
Halo is winning that poll as well btw :D