SC - blast suppressor and toughness are required.
HC - toughness is required.
SC - low profile is very beneficial since the most common streak used is the UAV.
Search and Destroy - lightweight helps to get map control.
Search and Destroy - blindeye is useful against people using tracking drones, which are somewhat common.
Gungho is pretty beneficial, but it's the first perk I tend to get rid of if I want to use something else in the class setup.
I don't use equipment very much, but if you're going to use grenades/semtex, then you'll need danger close to actually get a kill.