Ill talk about scoundrel, and necro. that are the only things i played after full release:

Scoundrel, best 3 in order:
1 - Backlash: do 85% damage, get backstab position, high range, only 1 ap? xD
2 - Mortal blow: use backlash to go behind target, use chameleon cloak, buff weapon with poison, instakill anyone for 2 ap. Of course it uses 3 SP, but just suck everyone u pass by and ure fine
3 - Sawtooth knife/rupture tendons: Rupture is great cuz AI is dumb and keep running/teleporting, otherwise it wouldnt be so good. Sawtooth gets ALL THE DAMAGE U WOULD DO summed it, and do it as piercing damage, and also sets bleeding, for only 2 ap, its easy to hit for tons of damage if u have both weapons coated with poison, having runes and then using venom coating skill.

Worst 3:

1 - Gag order
2 - Corrupted blade
3 - Fan of knives

obs: Wind up toy is good, just forget using most summons if u dont have summoning levels. Artillery plant can one-shot every enemy on the fight simultanely if u have 14+ summoning.

Necromancer:

Best 3:

Well necro use a lot of combos, but i will try to separate stuff.

1 - Raise Bone Widow: That crap is just too strong if u dont have any summoning levels, atleast for tanking.
2 - Bone Cage: Need 2k shields for 1ap? cool use that.
3 - Living on the edge: Pretty good, only 2 ap if u use elemental affinity.

Worst 3:

1 - Infect: Hey, disease that guy and your entire party, nothing can go wrong!
2 - Silencing stare: Its not that bad, but 2 ap just for silencing when ppl are out of magic armor is meh.
3 - Black Shroud: Same stuff.