Depends on what you want to do.
I have a few go-to ones (keep in mind that I mostly play HC infantry)
Ammo - Silencer - Launcher
type 115 + rco/spar 16 + rco/ak12 + rco
EOD skin unless it's an open AO, in that case I run whatever skin gives me decent armour and a mobility boost.
It's pretty much a one man army loadout.
Machinegunner - Silencer - launcher
Mk200 + rco/ spar16 s + rco/ mx-sw + rco/ lim85 + rco
Same as before but much more firepower.
Marksman - Ammo - Silencer
Cyrus + AMS/ Mar-10 + AMS
Yep, high calibre semi auto marksman rifles, for when I'm only expecting long range engagements inside the AO or when I'm trolling tower campers.
Designator - launcher - explosives
ADR97 + ACO red
Usually recon or VR suit.
Vehicle hunting loadout. Designator helps locating targets because of thermals, ADR is just because of good balance between weight and stopping power.
Marksman - Ammo - Indefatigable/Medic
APDS lynx + AMS
EOD or anything with some armour
Works the same as my cyrus/mar10 loadout but it's mostly to clear towers from a relatively safe spot.
Machinegunner - Marksman - Silencer
SPMG + AMS
Ghillie or diver suit (only on one particular map)
tear farming loadout, spmg is a 260 round full auto sniper rifle and is extremely quiet. Sit at the edge of the AO and pick targets. Watch the chat for salty ass people.
Machinegunner - Silencer - Indefatigable/Medic
Navid + rco
EOD or infantry
Another tear farming loadout, this is is more mobile and, along with the APDS, it's the only gun that can reliably kill those spec ops tryhards.
Machinegunner - Ammo - Medic
Zafir + ARCO or ACO
EOD or infantry
Zafir is the ultimate tryhard gun, a poor man's navid that I have absolutely no idea how to play. I use this when I stick to groups of people or need the last bit of experience to level up. I use the ARCO because the RCO clips into your clothing when you deploy the bipod and have a backpack, the ERCO sits too low and half reticle is blocked by the front iron sight. BI stated they fixed it a long time ago by moving the optic forward, but they never really did.
I rarely use spec ops, I find it broken AF and it should be removed asap.