Best...
...sweeper: Yeah,
Languish has to take the crown here. Tragic Arrogance gets an honorable mention for being able to decimate planeswalker.dec and keep your biggest threats alive.
...single target removal:
Declaration in Stone costing only 2 mana has proven to be good time and time again. Nature's Way is second, but quite a distant one.
...card draw spell:
Read the Bones. Take Inventory and Cathartic Reunion need deck support to be efficient, RtB is good in any deck you can cast it in. Not Glimmer of Genius good, but good.
...burn spell: Close call between Exquisite Firecraft and
Collective Defiance; I like the added flexibility of Defiance, though.
...ramp spell: Probably
Nissa's Pilgrimage; making sure to hit that land drop every turn.
...overall effect:
Dark Intimations is really powerful, no questions asked. Its only problem is the restrictive mana cost. Part the Waterveil might be second, but again, pretty distant second.
Overall: It's really tough to declare a winner here, as the sorceries really fill in the holes in decks that instants can't. At the end of the day I might just give the nod to
Languish for being a midrange/control staple and a massive reason to play Black.