My friends and I have had an argument about which is better, the Battle Rifle or the DMR. Im wondering which is better for what gametype and situation so I can prove to them that one weapon is better than the other for certain things. I also wondering what secondary weapon would go better (Magnum, Plasma Pistol, or Boltshot) with one of them for a combination during a match of BTB. If you guys could please respond that would be great.
BR with DMR on big maps.
BR with Assault Rifle on small to medium maps.
I will settle this with simple math and logic for you and your friend.
The Battle rifle kills in 4 shots, and is effective as a close-medium range weapon.
The DMR kills in 5 shots, and is effective at most ranges.
This means that the Battle Rifle is completely superior to the DMR at close range, but inferior at longer ranges.
I recommend a starting weapon of the Battle Rifle on small maps, and a DMR as a starting weapon in larger maps. Your secondary weapon is at your own discretion and playstyle.
First of all, it doesnt matter the weapon, the important thing is how you use it, but for answer your question, personally i prefer BR but for big maps is better the DMR. For secondary Weapon i use Magnum but for big maps use the plasma pistol is a good option because you can paralyze the vehicles and destroy them with bullets or a plasma grenade.
sorry if somebody don’t understand something. i speak spanish, but i try to speak it as understandable as possible 
BR
Short + Medium range? BR85 [Heavy Barrel Service Rifle].
Medium + Long range? M395 [Designated Marksman Rifle] (or the Z-250 [‘Light Rifle’].
…
Extreme range? Gauss hog/M6 Splaser/Z-750 [Special Application Sniper Rifle].
Secondary weapon is either the Plasma Pistol (lolno enemy vehicles that get too close- or, in VS AI games, noob combo darn near everything with shields), Z-110 [Directed Energy Pistol/Exotic] for CQC (thanks for the nerf, 343i!). The M6H Magnum is more for getting headshots if your primary weapon needs to reload.
BR is the best primary weapon on all maps but on Ragnarock, DMR would be better.
Secondary weapon you must choose the plasma pistil for destructing vehicules on BTB, but you must take magnum or Bolshot in small maps with no vehicules.
/!\ Bollshot is a noob weapon & DMR too 
I like the DMR and Plasma Pistol.
I like the BR, its fun and easy to use. the DMR takes a bit of skill to use and I find it really only good for SWAT and large maps. I quite like using the Magnum for the secondary, although the Plasma Pistol is useful for disabling large enemy vehicles (Mantis etc.) I’ve never used the Boltshot, can it kill in 1 shot? I heard its like a pocket shotgun? apart from that, I quite like using the Firepower tactical package and taking along an Assault Rifle or Suppressor.
The DMR is a solid weapon in my opinion. If you are a crack shot with it, it’s a surgical weapon
It depends on the map and your play style. However, best bet is carrying both at once. Or, if you are like me, spawning with one and taking the other from some jerk’s cold, dead hands.
BR since u can do also well with it on wide range