I tend to use the DMR for the mid to long range ability, along with active camo, explosions and grenades for the other catagories.
I like to slowly play the map but use the grenade abilities so when i get caught in rough situations i can take down enemy players with me:)
on the other hand i like taking a couple others and using the vehicles on the large maps, if you have a couple others who know what they are doing while driving or shooting you can pretty much dominate a big team infinety slayer match as long as there are no tanks or mechs.
Im still new at all this though so im trying out as much stuff as i can, not a serious player but more into having fun and could care less about my K/D ratio as long as im having fun.