I always run, Ghost, Cold Blooded, Blind eye, Engineer, and Scavenger. I run these because the enemy cannot see my GT or see me during a UAV, the Engineer is for seeing Shock charges, claymores ETC. Scavenger is because you can never have enough ammo. I am always finding myself out of ammo without scavenger, so to solve the problem, I run scavenger. There is no other way to play
90% of my classes have flak jacket, cold blooded, engineer... and most often i run perk 1 wildcard with ghost... also i always have black hat, and black hat coupled with engineer gives a huge strategical advantage often...
Scavenger is a must-have for me -- especially since I run LMGs the majority of the time. After that it's gotta be Engineer or something. I gotta have the tactical advantage over enemy equipment; I hate getting baked by Guardians if I can't see them LOL.
Hardline is a must for me. I usually Run Hardline with Ghost, Coldblooded, and Dexterity and/or engineer. I love me some EMP grenades also. and C4, C4 is my most used equipment.