I tried playing with the DMR. Didn't bother with it for long, back to the Lightrifle for larger BTB maps, the BR for smaller BTB maps.
I don't know why but i just can't use the DMR... i think i'm so used to the LR's 4-shot kill (combined with patched rapid ROF, that thing is excellent as long as you can keep the pressure up) that i fuck up the 5th shot or something.
Unscoped... it is okay but a bit meh. Very punishing, you miss one shot, you're dead. In this it is like the Carbine but the LR still feels better.
The Carbine, despite being awesome, is just plain bad. Bring back the goodness that was Halo 2 Carbine, with its rapid ROF, good accuracy and 7-kill shot.