They aren't particularly comparable in the way the gameplay works, and different entries in each series vary wildly in quality, and I also prefer Halo to both. However, if forced to pick one, I'd choose CoD, specifically CoD 4, which is the best of the series.
I'm going to be really honest here, I've played games on both sides, from battlefield: Bad company 1 & 2 and Battlefield 3 and 4. Now on the call of duty side, the games I've played would be black ops, black ops 2, ghosts and throwing in advanced warfare. Battlefield is really gets me because one, it's more realistic and has a better physics engine. Two, in game vehicles and you can fly helicopters to jets. Everything is about team work in this game and is truly way more intense. (now this is mostly opinion, so calm down.)
@SirLegendary It went very much downhill for CoD after Modern Warfare. To be fair, that's because it has the best campaign and I mostly only care about single player. If I want a multiplayer shooter, there's only one I consider: Team Fortress 2.
My favourite is Call of the duty games because of storyline, difficulty level and of course graphics. I never liked battlefield don't know the reason!My favourite in COD series would be COD MW 3
