I personally would like to see the DMR added just to get variety . Maybe even see the carbine added as, since some people who rock with a BR may not be as good with a DMR it would even out the playing field in the games and CSR I would think.
I'm guessing this is for Halo 5. So I'd say DMR with a reflex sight. So we don't have the spray problems the BR has. And it won't have the cross map advantage the normal DMR would have.