Ogre Mage
Hero
In terms of the best, I would consider it a tie between Agonizing Blast and Devil's Sight. I only run ranged warlocks so Agonizing Blast is essential. But Devil's Sight is good for all PCs, even those with normal darkvision. For human PCs it is big.
The worst is Sign of Ill Omen. Just terrible.
The worst is Sign of Ill Omen. Just terrible.