OK this isn't a flame war so don't post if you're just going to be a biased prick. We post the things we like about each game. I love the open, gritty feel of battlefield, it's intense in a patient more realistic way while I love the fast frantic precision of call of duty!
I honestly love both of them, dice and IW.
Though, not BF3.
BF 1942/3 is where my loves at for Dice.
As far as COD goes, treyarch made a unbelievable game when they made COD3 and WaW. Blackops sucks.
IW struck gold when they made MW, with a kickoff to a great story and good multiplayer. MW2 followed the same path, but things such as OMA were misused to spam tubes. Storyline was progressively better. Still needs the intel-based cheats like in cod4.
overall, their good game titles. MW3 is killing me with the wait, while BF3 looked like crap on the beta. It might be worth it after a year or so for PC.