FAT6 + Reviver3 = great healing obvs, but also after you revive bring them right back to full health. quickly too. FAT2 is a waste IMO
SharpEars3 + Agility3 = I believe sharp ears 3 is underrated. Im noticing less use of CT2 so with the fast crouch speed of agility it pairs nicely with being able to enter listen mode while still moving quickly. Great combo to flank easily.
Scavenger3 + Crafter3 = I know that the dropped supply is really random but if you can consitently get tons of kills, youll eventually get a good amount of extra materials for which you can craft more gifts. Also, who doesnt like more ammo??