You know when the DMR is NOT a good weapon? When you turn a corner and within two meters of you is a guy with the AR.
Right, so you should use a weapon with terrible range just in case some idiot player decides to turn a corner without checking it? Sorry, I'm not going to use a terrible weapon just so I can get one or two lucky kills.
This is why you get two weapons...
"Do not be to eager to deal out death and judgment, for even the very wise cannot see all ends." -Gandalf
Pro tip, children: Some weapons are completely viable in certain situations. It would behoove you to keep a bit of variety in your playstyle.
Automatics are not viable if you're playing good enough people.
I played 50 high Squad Battle, BTB, Slayer, Doubles, and Objective on a regular basis, and it was definitely viable in certain situations. Catching someone off guard for a second nets you a quick kill, and it also has a good chance of slightly enraging your opponent, and getting in their head for future engagements.
360 GT = Samuel Adams Part of the #1 Legendary 4-player ODST FireFight squad (with Pope Rex, UEG Panik, and mastercmj)