I'm guessing the option for both isn't viable. BF can be a much more tactical game with various people filling different roles on a team. The option between the different classes is what I find most appealing. You can roll with a squad of people where one person is healing everyone, another is supplying ammo and another is dealing with taking out or repairing vehicles. Because of that there's a lot more variation in the gameplay ultimately giving the player lots of options on how they want to play the game.
Obviously MW3's new pointstreak classes are trying to adopt a similar gameplay but BF definitely wins in that category. Another big thing is that CoD is known for its twitch finger playstyle. BF historically is much more open, so there's less of a need to play like that.
Overall they're both going to be great games, just very different from one another which is why the comparison between the two is pretty pointless.