SUPPORT
DMR - I use DMR because of the 1 shot precision burst which holds the aim more steadily. The range is incredible, as if you had small arms sniper rifle and the close range shots are accurate in the right hands. Love the DMR.
Assult Rifle - I use the Assault rifle because I find myself in a multi-kill situation many times, so when I have to reload my DMR I can just hit Y and switch to the Assault Rifle which is a nice weapon in close quarters and even medium distance. The ammo in this gun is amazing as well.
Plasma Nade - I use Plasma Grenades for sticking vehicles. I also like these nades because they land and STAY exactly where you want them to be 99% of the time (so they are more accurate in my own opinion), and lastly they are awesome if you are in a firefight and about to die you can just stick the other guy to make it an even 1 kill to the 1 death.
Promethean Vision - I can tell where other players are before they hit the radar, I can see where nades are being thrown/landing, This also allows me to get the first shot on a gun running around the corner. Very nice ability.
Firepower- This is what allows me to use my Assault rifle for secondary weapon!
Ammo - I always used to run out of ammo, more ammo = more kills!