Ive always liked the carbine more than BR but it has that annoying tendency to shoot a stray round every once in awhile so I stuck with BR. Havent played much 4 cuz I didn't like the map design in reach or the AA's.
I roll DMR. Midrange surgery and dominance, especially post-update. It is like firing a scalpel, and requires the same degree of deliberate control, unlike the BR, which is like training wheels for the big-boy bike of the DMR.