Personally, I love Call of Duty over Battlefield. However, I would almost have to say they are equally great, but in different aspects. Call of Duty is a little quicker paced, but this is because the maps are smaller. Battlefield is massive. The maps are insanely huge, and you have the ability to drive land and aquatic vehicles, along with flying planes and helicopters. Being a sniper in Battlefield is much harder also, which I enjoyed when I sniped, or was being sniped at. In Call of Duty, it doesn't matter in which direction a player is moving, or their distance, as long as you have the crosshairs on them when you pull the trigger, they are more than likely dead. This is not the case in Battlefield. You have to adjust your aim higher for greater distances, and if they are walking or running, you have to aim ahead of them. I love the feel and/or flow of Call of Duty. I also love how Battlefield is more realistic. My final choice will always be Call of Duty. Also, I have always wanted to see Call of Duty keep the same feel so to speak, but incorporate everything that Battlefield has to offer, such as realism, massive maps and the ability to drive/fly vehicles.
Having played both, Call of Duty is a fast paced game, having small maps and fast times to kill. Meanwhile, Battlefield tried their best to replicate real life modern warfare, using bullet time, bullet drop, and vehicles used in the army today. If you like more realistic shooters, go say hi to Dice and go play battlefield. If you like super tense fast paced games, go meet up with Treyarch. I personally prefer battlefield because of the bullet mechanics, like the bullet time and drop. It makes it fun for me actually do some hard core sniping about 1000 meters away, landing head shots and feeling super satisfied. As for Call of Duty, some people just shake their head and wonder why there's even snipers in the game because of the tiny maps. I'm not gonna lie though, this was a tough call for me, loving both games.