I like the carbine a lot, but don't always feel in the mood to use it.
I have been loving the BR as of late though. I love just being able to swipe for the last headshot.
It is much better than the DMR at Mid-close range in my opinion.
I like the Carbine though because you can just harass enemies with its rate of fire, it is accurate, and can kill fast if you hit shots. I think the carbine benefits more from aggressive play than the BR does.
I haven't used it much, but lately I have tried out the LightRifle and that weapon has a huge amount of potential. Its scoped damage, along with its burst function from the hip makes it a threat at any range you can hit with zoom and easier to use than the DMR at mid-close range. It just feels so clunky though, which takes some time to get used to.
The more I play, the more I see that the weapons are balanced better than they first appear. Though, if the DMRs fire rate was slowed ever, EVER, so slightly, it would be perfect. Even doing that might mess things up though. --- http://www.last.fm/user/BigRobb/
DMR has to be the go-to. Not big fan of the BR but I can see its uses for defending a base or mid-close range encounters. Carbine is useless, and light rife is great on long-sight maps like ragnarok so I do often use it for that (to chip away at the commendation,) but even then the DMR competes very closely with it, and is probably better to have in case someone sneaks up on you. --- And this stillness of life did not in the least resemble a peace. It was the stillness of an implacable force brooding over an inscrutable intention.