I levelled healing op from level 10, it's pretty OP in my opinion and the 2man quests were easily solable. Just make sure you gt some gear for Kaliyo, put her into defnsive and (on the bigger groups with hard/leets) untick her grenade and emp blast aoe abilities to stop breaking sleep dart/flash bang. I put a Kolto probe on Kaliyo first as she takes the majority of damage. (and to get ta procs) I then send her in while I'm casting a snipe. If you cast explosive probe straight after, the probe explodes as the snipe hits, one shotting a lot of mobs until you get higher. Then run in, shiv, barrage, nade. When you get higher, ambush is pretty sweet with eviscerate. Use Corrosive dart on hard or leet mobs, you should kill them just as it expires so is a good use. When you get higher, groups of 4 are cannonfodder with orbital strike. esecially as you can cast, stealth ambush (while orbital strike hits 1st blast) nade a mob back into the blast radius, stun another, barrage, all dead. Sometimes without taking a single hit. Epic.