When a curse is so damn nice, you sometimes don't even want to kill the cursed creature:
Death Link.
Honestly though, with enchantments, it's really hard to choose, because they do just about anything.
Standard bearer is the reason I play Warlord.
Mongoose makes my solos work.
Enfeeble makes headaches go away.
Barkskin is the reason I play druid.
Still. Death Link takes the cake for me.